A METHOD AND A DEVICE FOR DEACTIVATING AN ALARM ELEMENT

Abstract: A method to deactivate a burglar proof system alarm element (1), the alarm element being adapted to be detected in an alternating magnetic field (2) in a scanning area (3) in the system, in that by means of a signal generator (4) provided in the alarm element it emits detectable signals (5) in said alternating field including a magnetization of a deactivator (4') thereby preventing the emission of said detectable signals. The method is especially characterized in that the deactivation of the alarm element (1) is achieved by means of a magnetizing impulse (11) directly in connection with a detection of the alarm element, the deactivation then being achieved by means of a magnetic field being essentially stronger than the magnetic field during the detection and with essentially the same direction. The invention is also related to a device for deactivation.

Description: A METHOD AND A DEVICE FOR DEACTIVATING AN ALARM ELEMENT The present invention relates to a method to deactivate a burglar proof system alarm element, the alarm element being adapted to be detected in an alternating magnetic field in a scanning area in the system, in that it by means of a signal generator provided in the alarm element emits detectable signals in said alternating field including a deactivation of the alarm element by means of magnetizing a deactivator comprised in the alarm element. Burglar proof systems generally of the kind mentioned above are already known in the art. See e.g. EP-A1-0,448,910 and US-A-3,820,104. A problem with these kind of systems is to achieve a safe deactivation, e.g. provided in connection with that a burglar proof item is paid for, such as an article of clothing. It is of course not desirable that an alarm is initiated in spite of that a payment had been made and the deactivation is intended to have been made. In using permanent magnets to magnetize the deactivator there is a risque that the deactivator is magnetized first and is thereafter demagnetized in that the alarm element is exposed for a field alternating the direction at the alarm element passage over the permanent magnets. If the relation between the field forces is unfavourable a B-H-loop is passed so that the remaining magnetization is not sufficient for a deactivation. A deactivation by means of a short current through the coil has not the above mentioned drawback as the field does not alternate in direction. However, a large amount of ferric magnetic material is required in the deactivator as the field direction might be unfavourable in relation to the deactivator. Thereby drawbacks are encountered i.a. in form of undesirable mechanical properties of the alarm clement. The present invention relates to a method and a device by means of which a reliable magnetization/deactivation is achieved without the drawbacks known in the art. Thus the invention relates to a method according to the ingressing part of the attached claim 1. The method is especially characterized in what is specified in the characterizing part of said claim. Moreover, the invention relates to a device according to the ingressing part of the attached claim 4. The device is especially characterized in what is specified in the characterizing part of aid last mentioned claim. The invention will be described herein below in more detail in connection to the attached drawing, on which - Figure 1 shows schematically a first embodiment of the device according to the invention in connection with a market cash register, and - Figure 2 shows schematically and in principle a lay-out of the arrangement of the device to detect and to deactivate alarm elements. In the device for deactivation according to the invention shown in the figures 1 designates a burglar proof system alarm clement, which in a way known per sc is adapted to be detected in an alternating magnetic field 2 in a scanning area 3 in that it by means of a signal generator 4 provided in the alarm clement emits detectable signals 5 in said alternating field. The deactivation of the element 1, e.g. in connection with a payment being made for an object 6 provided with the alarm clement 1 in a cash register 7 or similar, comprising a magnetization of a deactivator 4' included in the alarm element, the emission of said detectable signals related to the alternating magnetic field is prohibited. With 8 is designated at least one coil, in the shown example illustrated with stretched lines and arranged under a hauling track 9 close to a cash register 7. With 10 is designated a control unit, which is shown more in detail in figure 2, adapted to receive signals from a receiver coil 5' for said detectable signals 5 for detecting an alarm clement 1 and to emit a deactivating magnetic impulse 11 directly when the alarm element is detected, the deactivation thus being adapted to be achieved by means of a magnetic field being essentially stronger than the magnetic field during the detection and with essentially the same direction. The control unit 10 comprises thus a detector 12, adapted to be supplied with received signals 5, a supply unit 13 for the coil arrangement 8 to achieve the alternating magnetic field as well as devices 14 to emit, preferably by means of discharging a capacity element 15, a deactivating magnetic impulse 11 to the coil arrangement 8. With 15' is designated a diode adapted to ascertain that the current through the coil docs not change its direction in that the coil and the capacitor arc forming a resonance circuit. With 16 is designated a switch e.g. elcctromagnctically operated and adapted to either connect the supply unit 13 or the devices 14 emitting said magnetizing impulse to the coil 8. The detector 12 is adapted to emit a short control signal 17 to the switch 16 when detecting any alarm clement, the switch lacking a control signal then being adapted to maintain the supply unit 13 connected to the coil arrangement and the switch being adapted to alternate so that the supply unit is disconnected and the devices emitting magnetic impulses 11 arc connected to the coil arrangement, the deactivating magnetic impulse 11 then being adapted to be emitted. Acccording to preferred embodiments, e.g. according to figures 1 and 2, the existing coil arrangement is adapted to provide both the alternating magnetic field for a detection and the deactivating magnetic field for magnetizing the deactivator, the deactivating magnetic impulse then being adapted to be emitted to said coil arrangement and the magnetizing field to be provided by means of said coil arrangement. The coil arrangement is preferably adapted to generate an alternating magnetic field with a direction varying with the alarm element transfer direction during deactivation with the object to have a favourable direction for magnetizing the alarm element in relation to the alarm element at least once during the transfer. According to an embodiment the coil arrangement comprises one coil with a configuration generally paralleltrapezoidic in the coil winding direction as shown in the figures. Normally the magnetization both during a detection and during a deactivation occurs preferably essentially parallel to the alarm clement longitudinal axis, which will occur by means of a suitable design of the coil arrangement at least once during the passage of the alarm element through the coil arrangement. The method as well as the function of the device according to the invention is essentially evident from what has been stated above. Thus, the deactivation of an alarm clement is provided by means of a magnetization directly in connection to a detection of the alarm element and preferably with the same coil arrangement, the alarm element then being deactivatingly magnetized, when it has a favourable direction in relation to the coil arrangement, when a favourable direction is required for a detection, and when the direction will be essentially the same during detection and during deactivation in that a deactivating impulse is emitted directly in connection with a satisfying detection of the alarm element. As also should be evident from what has been stated previously the invention provides essential advantages compared with what was known in the art. Thus, a large deactivation safety is achieved as the alarm elements favourable direction in relation to the deactivating magnetic field is scanned and is ascertained by means of the detection preceding the deactivation. In this way also moderately magnetizing fields can be used during a deactivation. The invention has been described above in connection with execution examples. Further embodiments and minor changes and amplifications might of course be envisaged without leaving the scope of the inventive idea. To achieve a desired function an alarm element is thus designed in such a way as indicated in the documents mentioned in the beginning, i.e. the alarm element includes both a signal generator of a ferric magnetic material with a relatively low coecivity and a high permeability, i.e. a comparatively easily saturated material and a deactivator including a ferric magnetic material with a higher coecivity than the material in said signal generator, the deactivator then being in a magnetized state preventing the generation of desired detectable signals by means of the signal generator. Therefore, the invention is considered not be limited to the embodiments stated above and might be modified within the scope of the attached claims.

Claims: Claims 1. A method to deactivate a burglar proof system alarm element, the alarm element being adapted to be detected in an alternating magnetic field in a scanning area in the system, in that it by means of a signal generator provided in the alarm element emits detectable signals in said alternating field including a magnetization of a deactivator thereby preventing the emission of said detectable signals, characterized in that the deactivation of the alarm element (1) is achieved by means of a magnetizing impulse (11) directly in connection with a detection of the alarm element, the deactivation then being achieved by means of a magnetic field being essentially stronger than the magnetic field during the detection and with essentially the same direction. 2. A method according to claim 1, characterized in that the magnetic field for a detection and the magnetic field for a deactivation arc provided by means of the same coil arrangement (8). 3. A method according to claim 1 or 2, characterized in that the alarm clement is transferred in an alternating magnetic field, having an alternating direction along the transfer direction of the element, e.g. a magnetic field generated by means of at least one coil (8) with a paralleltrapezoidic configuration in the coil winding plane. 4. A device to deactivate a burglar proof system alarm element, the alarm element being adapted to be detected in an alternating magnetic field in a scanning area in the system, in that it by means of a signal generator provided in the alarm clement emits detectable signals in said alternating field, devices being provided to magnetize a deactivator included in the alarm element thereby preventing the emission of said detectable signals, characterized in devices (12 to 16) to detect an alarm clement (1) and to emit a deactivating magnetizing impulse (11) directly in connection with a detection of the alarm clement, the deactivation thereby being adapted to be provided by means of a magnetic field being essentially stronger than the detecting magnetic field and with essentially the same direction. 5. A device according to claim I, characterized in only one coil arrangement (8) for the detection and the deactivation. 6. A device according to claim 4 or 5, characterized in devices (8, 13) for generating an alternating magnetic field with a direction varying with the adapted transfer direction of the alarm element during deactivation. 7. A device according to claim 6, characterized in that the devices for generating said magnetic field include at least one coil (8) with an essentially paralleltrapezoidic configuration in the coil winding direction.

Inventors: AASBRINK LEIF, AASBRINK, LEIF
Applicants: AASBRINK LEIF, AASBRINK, LEIF
Application year: 1997
Main classification: G08B13
IPC codes: G08B13