EP0136265B1 - Resonant circuit for theft protection of articles, method of making such circuits and device for carrying out the method - Google Patents

Abstract

1. Oscillatory circuit, for an article to be secured against theft, with a winding (7) formed of an insulated electrical conductor (11) and a capacitor (5) connected in parallel thereto, characterised thereby, that the capacitor (5) is formed by likewise insulated portions (11b, 11c) of the conductor (11) forming the winding (7), which portions adjoin both ends of the winding (7) and are twisted together.

Description

The invention relates to a resonant circuit according to the preamble of claim 1.

It is known to provide goods intended for sale in retail stores with a parallel anti-theft circuit which is often designed as a label and has some type of printing. At the exits of the sales rooms, there are monitoring devices to be passed by the customers, which have means for generating a high-frequency alternating field with alternating increasing and decreasing frequency and for detecting the field. If the goods are properly paid for, the resonant circuits will either be removed or destroyed by the checkout staff. If, on the other hand, a customer passes a monitoring device with a product that still has an intact oscillating circuit, he withdraws energy from the electromagnetic field during resonance and radiates some of it again, which can be determined by the monitoring device.

Known parallel anti-theft circuits have an air coil, the winding of which consists of an electrical conductor insulated with a web, with adjacent turns being connected to one another with a binding agent, so that the winding is self-supporting. The resonant circuits also have a capacitor with ceramic insulation, the terminals of the capacitor being connected to the winding ends in an electrically conductive manner with crimped or soldered connections. When manufacturing these resonant circuits, windings must therefore be wound and their turns connected to one another by means of a binding agent. Furthermore, relatively expensive ceramic capacitors have to be manufactured or procured and connected to the winding ends. Finally, it must be checked whether the resonance frequency has the intended setpoint. These resonant circuits are therefore also relatively expensive to manufacture in very large series, which is particularly disadvantageous if the resonant circles are discarded or destroyed when the goods are paid for.

Furthermore, DE-B-28 26 861 discloses a parallel resonant circuit with a two-part plastic plate and a bare wire arranged in a spiral groove of the one plate part. This forms a coil, the ends of which are connected to the connections of a capacitor of a conventional type. This resonant circuit has largely similar disadvantages to the resonant circuits described above and additionally the disadvantages that it is not bendable and is therefore unsuitable for certain applications and that the capacitor connection still has to be insulated from the coil winding with an insulating film to be applied in a special operation.

Furthermore, for example from WO-A-83 / 01-697 resonant circuits with a plastic film are known, in which the coil and the capacitor are formed by coatings applied to the plastic film. Although these resonant circuits can be produced at lower costs than the previously described, a winding consisting of a conductor insulated with a web and a ceramic capacitor having resonant circuits, they are still relatively expensive. Furthermore, the resonant circuits formed by a coated film have only a relatively low quality factor, for example in the range from 50 to 70. Such a low quality factor has the disadvantage that the resonant circuits cause only a very slight change in the high-frequency field when passing through the monitoring device. This in turn means that in many cases the monitoring device does not detect the passing of an oscillating circuit, so that, for example, approximately half of the thefts do not trigger an alarm signal.

The invention has now set itself the task of creating a parallel resonant circuit which is both inexpensive to manufacture and has a good enough quality factor for reliable theft detection.

This object is achieved by a resonant circuit of the type mentioned in the introduction, which according to the invention is characterized by the features of the characterizing part of claim 1. Advantageous further developments of the resonant circuit result from claims 2 and 3.

The invention further relates to a method for producing a parallel resonant circuit according to the preamble of claim 4. According to the invention, the method is characterized by the features of the characterizing part of claim 4. Expedient refinements of the method emerge from claims 5 to 8.

The invention further relates to a device for carrying out the method according to claim 5 according to the preamble of claim 9. The device is characterized according to the invention by the features of the characterizing part of claim 9. An advantageous embodiment of the device results from claim 10.

• die Figur 1 eine schematische Draufsicht auf einen Schwingkreis, wobei der Leiter zur Verdeutlichung mit übertriebener Dicke dargestellt wurde,
• die Figur 2 einen schematisierten Schnitt durch die miteinander verdrillten Abschnitte des isolierten Leiters, in grösserem Massstab, und
• die Figur 3 eine schematisierte, nicht massstäbliche, teilweise im Schnitt gezeichnete Darstellung einer Einrichtung zur Herstellung von Schwingkreisen.

The invention will now be explained on the basis of an exemplary embodiment of a resonant circuit shown in the drawing and a device used for the manufacture of resonant circuits, wherein all of the features and combinations of features disclosed below, in particular insofar as they are new, can also be considered essential to the invention. In the drawing shows

• Figure 1 is a schematic plan view of a resonant circuit, the conductor for Ver clarification was shown with exaggerated thickness,
• 2 shows a schematic section through the twisted sections of the insulated conductor, on a larger scale, and
• 3 shows a schematic, not to scale, partially drawn in section of a device for producing resonant circuits.

The electrical parallel resonant circuit shown in FIG. 1, designated as a whole by 1, has an air coil 3 and a capacitor 5. The coil 3 is without a bobbin and therefore consists of a self-supporting, approximately circular winding 7, which is formed from a section 11 of an insulated electrical conductor 11. The coil 3 is designed as a flat coil, i. H. all of its turns are spiral along a plane perpendicular to the coil axis. The end section 11b of the insulated conductor 11 which is connected to the conductor section 11a at the inner end of the winding 7 and the end section 11c of the conductor 11 which is connected to the conductor section 11a a at the outer end of the winding 7 are strongly twisted together and form the capacitor 5 .

As can be seen from FIG. 2, the insulated electrical conductor 11 has an electrically conductive, metallic core 13, which is preferably formed by a full copper wire with a circular cross section. The insulated conductor 11 also has an insulation 15 made of plastic and enveloping the core 13. The insulation should have only a small dielectric loss factor in the high frequency range. Furthermore, at least the outer part of the insulation 15 should preferably consist of a weldable thermoplastic, namely approximately a weldable polyolefin. The inner, most part of the insulation 15 can consist, for example, of polypropylene with a dielectric loss factor of 0.000 5. This inner jacket can be provided on the outside with a thin, easily weldable polyolefin copolymer layer. However, the insulation can also consist entirely of weldable polyethylene.

The isolation sections from adjacent, i.e. H. Successive turns of the winding 7 are connected to one another at their contact points, namely welded. In contrast, the insulation sections of the twisted conductor sections 11b, 11c are preferably not welded, so that the two conductor sections 11b, 11c hold one another only by their twisting and mutual wrapping.

The contacting portions of the conductor 11 are complete, i. H. in particular also at the free ends of the twisted sections 11b, 11c, electrically insulated from one another. The resonant circuit 1 thus forms an open parallel resonant circuit in which the coil 3 and the capacitor 5 are electrically connected in parallel with one another and are otherwise not electrically connected to anything. The resonant circuit therefore consists exclusively of a one-piece, coherent, insulated conductor.

The twisted together conductor sections 11 b, 11 c are expediently arranged in the circular opening of the coil delimited by the winding.

The oscillating circuits are provided to secure goods against theft which are intended for sale in sales shops, in particular retail shops, self-service shops, department stores and the like. The resonant circuits are attached to these goods as an appendage. The resonant circuits can be used, for example, in bags or fastened, for example glued, to flat pieces of plastic, paper or cardboard. These bags or flat pieces can, for example, be provided with an imprint which contains a description of the goods and / or a price or the like. The resonant circuits can also be glued directly to the packaging of the goods or attached in some other way. Since they can be manufactured at a low cost in a manner yet to be explained, they are very well suited for applications in which they are used only once and are either thrown away or destroyed by the checkout staff if the goods are properly paid for.

The outside diameter of the winding 7 can be, for example, 3 to 10 cm and the number of turns can be approximately between 4 and 15 and, for example, 5 to 9. The metallic core 13 of the conductor, i.e. H. the actual wire has a diameter d of preferably about 0.2 to 0.5 mm and for example 0.25 to 0.35 mm. The thickness or sheath thickness s of the insulation 15 is preferably at most 0.1 mm and, for example, about 0.02 to 0.05 mm.

The resonance frequency of the resonant circuit should be in the high-frequency range according to the anti-theft monitoring device provided and can be between about 5 MHz and 15 MHz. If, for example, the transmitter of the monitoring device generates signals with frequencies fluctuating between 8 and 8.5 MHz, the resonance frequency of the resonant circuits should lie in this area and preferably approximately in the middle thereof. So that the resonance frequency of an oscillating circuit is not excessively changed by interference capacitors, the capacitance of the capacitor should expediently be at least 20 pF and preferably at least 25 pF and for example approximately 30 pF to 40 pF. If the core 13 and in particular the insulation 15 have approximately the cross-sectional dimensions given above, capacities of these sizes can be achieved. if the twisted together conductor sections 11b, 11c in the untwisted state have a length of about 5 to 20 cm and the length in the twisted state then at most 70% and for example at most or about 50% of the original length. Each conductor section 11b, 11c then forms at least about 10 and for example about 20 to 50 turns. (For reasons of drawing, FIG. 1 shows the conductor with an exaggerated thickness and, accordingly, only a relatively small number of twisted turns.)

The quality factor of the resonant circuit is at least 200 and, for example, 250 to 350.

The coil 7 forming the coil 3 is relatively dimensionally stable with respect to forces which act on it along the plane spanned by it. If, on the other hand, a torque is generated by a pair of forces acting on the coil, which torque can be represented by an axial vector lying in the surface spanned by the coil, the flat surface originally spanned by the coil can within certain limits become a curved surface relatively easily be deformed. This enables the resonant circuits, when used for theft protection, to also be attached to goods for which they should have a certain flexibility, and ensures. nevertheless a sufficient constancy of the resonance frequency.

The highly schematized and simplified device shown in FIG. 3 and used to produce resonant circuits has a frame 21 on which a drive device 23 with an electric motor and a shaft rotatably mounted about an axis of rotation 25 is arranged. A coil winding carrier 27 has a rotor 29 which is fixed in terms of rotation and preferably rigidly to the shaft, and a flange 31. The latter can be brought from the winding position shown in FIG. 3, for winding a coil, in which it is rigidly connected to the rotor 29, into an ejection position, for ejecting a coil, in which it is partially or completely is separated from the rotor 29. The flange 31 has a projection 31a in the inner part of its end face facing the rotor 29, which protrudes into a recess in the rotor 29. Outside of the projection 31a, the rotor 29 and the flange 31 have radial annular surfaces facing one another. A radial annular gap 33 is present between them, the axially measured width of which is approximately equal to the outer diameter of the insulation 15 of the conductor 11. It should be noted here that the diameter of the conductor 11 and the width of the gap 33 in FIG. 3 have been shown with an exaggerated size for clarification. The collar 31 of the flange 31 projecting beyond the projection 31a is provided at one point on its circumferential surface with an incision 31b which extends approximately up to the projection 31a in the radial direction. The rotor 29 and the flange 31 are provided in the centers of their mutually facing end faces with holding parts 35 and 37, respectively, which hold the flange rigidly and in particular non-rotatably, but releasably on the rotor. The holding parts 35, 37 can be formed, for example, by ferromagnetic bodies, at least one of which is designed as a permanent magnet. Apart from the holding parts 35, 37, the rotor 29 and the flange 31 consist at least essentially of electrically insulating, non-magnetic material, for example plastic.

At least one guide 43 is fastened to a part 41 of the frame 21, which guides a slide 45 on the side of the flange 31 facing away from the rotor 29, which can be displaced parallel to the axis of rotation 25. Furthermore, there is at least one spring 47 acting on part 41 or another part of the frame 21 and on the slide 45, which exerts a force directed away from the rotor 29 on the slide 45 and presses it against a stop 49 arranged on the frame, for example adjustable, into the in FIG the position shown in Figure 3 pulls. A holding, contacting and cutting device is present on the slide 45, which has a support 51 and two holding, contacting and cutting members 53, 55 arranged on sides facing away from it. Each holding, contact and cutting member 53, 55 has a guiding and actuating device 57 or 65 fastened to the slide 45, a bolt-like part 59 or slidably guided, namely displaceable approximately at right angles to the axis of rotation 25 in the device 57 or 65. 67 and a spring 61 and 69 respectively. The two bolt-like parts 59 and 67 are provided with cutting edges at their ends facing the support part 51 and the springs 61, 69 engage the parts 59 and 67 in such a way that they can press them against the support 51.

The two guiding and actuating devices 57 and 65 have electrically and / or possibly pneumatically controllable actuating means, so that they move the associated bolt-like part 59 or 67 away from the support 51 into a position against the force exerted by the spring 61 or 69 can move in which the conductor 11 used to produce the resonant circuits can be inserted between the support 51 and the bolt-like part 59 or 67. Then when the guiding and actuating devices 57, 65 release the parts 59, 67, the latter are pressed by the springs 61 and 69 against the support 51. The force generated by the springs is dimensioned such that the parts 59, 67 clamp the insulated conductor 11 and that their cutting edges penetrate the part of the conductor insulation 15 facing them and come into contact with the electrically conductive core 13 of the conductor 11. The actuating means of the two guiding and actuating devices 57, 65 are also designed such that they can move the parts 59 and 67 abruptly against the support 51 with a force sufficient to completely cut through the insulated conductor 11.

In the frame 21, a supply coil 63 is rotatably mounted with schematically indicated bearings, which supply a supply of the insulated electrical conductor 11 contains and which may be connected to a controllable unwind drive. Furthermore, a number of conductor guide means 85 serving to guide and move the conductor 11 are held on the frame 21, which are indicated only schematically in FIG. 3 by a dash-dotted element and are at least partially movable, being actuated by electrically or pneumatically actuated actuators and can be moved. Furthermore, there is also an electrically or pneumatically actuable flange adjustment device 91 arranged on the frame 21, of which a part is only schematically indicated by dash-dotted lines in FIG. 3. In addition, sensors, limit switches and the like can also be present in order to determine the positions of movable elements of the device.

A control device designated as a whole as 71 has a program control part 73 with electronic and possibly additional pneumatic control means, an electronic frequency meter 75, an electronic frequency comparator 77, a preferably controllable, for example switchable and / or switchable and / or adjustable, welding current source 79 and a controllable, for example switch 81 formed by an electromagnetic relay. The components mentioned and also belonging to the control device can be arranged centrally in the same device or else distributed at different points in the device used for producing the resonant circuit, shown in FIG. 3.

The bolt-like part 59 belonging to the holding, contacting and cutting member 53 consists at least at its cutting end of an electrically conductive metal, but is insulated from the frame 21 and the electrical ground of the device and is connected to the changeover switch 81 by an electrical connection , through which it can be connected either to the frequency meter 75 or the welding current source 79. The bolt-like part 67 belonging to the holding, contacting and cutting member 55 is also at least at its cutting-side end electrically conductive and is connected by electrical connections to the electrical ground and the ground connections of the frequency meter 75 and the welding current source 79. The frequency meter 75 and the welding current source 79 are electrically connected to the program control part 73 and can be switched on and off by this. The controllable changeover switch 81, formed for example by a relay, is likewise connected to the program control part 73 and can be controlled by the latter. The frequency comparator 77 has an input connected to the frequency meter 75 and an output connected to the program control part 73. The program control part 73 is also connected to the drive device 23, the guiding and actuating devices 57 and 65, possibly existing sensors and limit switches for monitoring the operating state, the actuating members of the adjustable conductor guiding means 85 and the flange adjusting device 91.

The automatic production of resonant circuits 1 by means of the device shown in FIG. 3 will now be explained.

First, the program control part 73 controls the conductor guide means 85 in such a way that they thread the conductor 11, which is used to form the resonant circuits, into the stationary coil winding carrier 27, which is in a predetermined rotational position. The conductor is inserted or drawn into the annular gap 33 and the incision 31 b. Furthermore, the conductor guide means 85 and the holding, contact and cutting member 53 are controlled in such a way that the free end of the conductor 11 is brought into the position shown in FIG. 3 and is clamped to the support 51 by the bolt-like part 59. On the other hand, the part of the conductor 11 running from the coil winding carrier 27 to the supply coil 63 is not yet clamped by the part 67 to the support 51 in the manner shown in FIG. 3, but rather is supplied by the conductor guide means 85 to the annular gap 33 approximately radially to the axis of rotation 25, so that it can run well into the annular gap 33.

When the conductor 11 is threaded in this way, the program control part 73 temporarily switches on the drive device 23, so that the coil winding support 27 is rotated about the axis of rotation 25 and in the process a winding 7 with the predetermined number of turns is wound from the conductor 11 in the annular gap 33 becomes. At the end of this winding process, the coil winding carrier 27 is brought to a standstill in a predetermined rotational position. Thereafter, the program control part 73 controls the conductor guide means 85 and the holding, contact and cutting member 55 such that the conductor guide means guide the part of the insulated conductor 11 extending from the coil winding carrier 27 to the supply coil 63 between the support 51 and the part 67 and the latter clamps the conductor 11 in the manner shown in FIG. 3 on the support 51. The support 51 and the parts 59 and 67 are preferably arranged in such a way that they hold the conductor sections 11b, 11c at stopping points which are arranged as close as possible to the axis of rotation 25 and at least approximately symmetrically to the latter.

The two bolt-like parts 59 and 67 also produce an electrical connection with the core 13 of the conductor sections 11b, 11c in this manufacturing phase. The program control part 73 now controls the changeover switch 81 and, if necessary, additionally the welding current source 79 in such a way that the conductor section 11b is temporarily connected in an electrically conductive manner to the welding current source 79 and this conducts a current through the two bolt-like parts 59, 67 during a time interval conducts the winding formed. The size of the energy supplied in this way becomes fixed in such a way that the insulation 15 of the successive turns of the conductor 11 held by the coil winding carrier 27 is welded. The energy supplied can either be predefined or regulated by regulating means. For example, a power of approximately 100 watts can be supplied during an approximately 1 second time interval. It is possible that the coil winding carrier 27 and the winding 7 held by it can be temporarily cooled by an air flow after welding.

The program control part 73 then puts the drive device 23 into operation again, so that the coil winding support 27 rotates the coil winding held by it about the axis of rotation 25 coinciding with its central axis. As a result of this rotation of the coil winding carrier 27, the sections 11b, 11c of the conductor 11 which extend from the two ends of the winding 7 to the bolt-like parts 59 and 67 are twisted together. When the conductor sections 11b, 11c are twisted, they are shortened and the slide 45 is pulled along the guides 43 toward the coil winding carrier 27. The counterforce exerted by the spring or springs 47 on the slide 45 always keeps the conductor sections 11b, 11c under a certain tension.

The electrically conductive cores 13 of the conductor sections 11b, 11c of the resonant circuit currently being manufactured become electrically conductive before or during the start of the twisting process or at least during the last part thereof via the bolt-like parts 59 and 67 and the changeover switch 81 connected to the oscillation frequency meter 75. This contains an oscillator whose resonant circuit is formed by the resonant circuit that is currently being manufactured. The program control part 73 puts this oscillator into operation at least during the last part of the twisting process, so that the resonant circuit oscillates at its resonance frequency. Since the capacitance of the capacitor of the resonant circuit increases as the twisting progresses, the resonance frequency decreases during the twisting. The resonance frequency is measured continuously or intermittently and compared by the frequency comparator 77 with an adjustable, predetermined target or limit value. On the basis of this frequency comparison, the program control part 73 stops the drive device 23 when the resonance frequency has decreased to such an extent that it is approximately equal to the predetermined target limit value and / or at most equal to the predetermined limit value. If it is permitted that the resonance frequency may also be a little lower than the specified target or limit value, the program control part 73 can let the coil winding carrier 27 continue to rotate after the resonance frequency has dropped to the predetermined target or limit value until the The next time the coil winding carrier with the winding 7 held by it reaches a predetermined rotational position, so that the coil winding carrier 27 is brought to a standstill in a predetermined rotational position. The number of turns of the twisted conductor sections 11b, 11c which enclose one another and thus also the capacitance of the capacitor 5 are thus determined on the basis of the resonance frequency measurement carried out during the twisting and the comparison of the measured resonance frequency with a predetermined target or limit value.

Since the resonant circuit is not in the empty space during the twisting process, but is held by the coil winding support 27, and because other parts of the device used for producing the resonant circuit are located in the vicinity of the resonant circuit held by the coil winding carrier, it does not have the same resonance frequency as he would have in the empty room. In general, the elements of the device will slightly increase the capacitance and possibly also the inductance of the resonant circuit. The limit value mentioned is accordingly set lower than the resonance frequency that the resonant circuit should have when it is used after completion. The size of the limit value to be set can be determined by a few tests. It should also be pointed out that the supply of conductors on the supply coil 63, which is still connected to the resonant circuit during the frequency measurement, decreases in the course of the manufacturing process. However, this decrease in the supply of conductors has practically no influence on the frequency measurement, because the end of the oscillating circuit connected to the supply coil is connected to the electrical ground.

When or after the end of the twisting process, the conductor 11 is gripped between the supply spool 63 and the bolt-like part 67 in the vicinity of the latter with a gripper of the conductor guide means 85 and cut through the two bolt-like parts 59 and 67. Furthermore, the, for example, gripper-like flange adjustment device 91 now grips the flange 31 and moves it at least partially away from the rotor 29, as a result of which the coil produced is ejected from the coil winding carrier 27. The flange 31 is then reconnected to the rotor 29. The manufacturing cycle then begins anew and another resonant circuit is produced again.

In this way, resonant circuits 1 which have a relatively high quality factor can be produced quickly and inexpensively. Since the resonance frequency is measured during the control of the twisting process, the resonant circuits also have a resonance frequency which is within a relatively narrow tolerance range after completion, so that a special manufacturing control and measurement of the resonance frequency after manufacture are not necessary. For example, it can easily achieved that the resonance frequency is in a range deviating at most ± 1% from a predetermined setpoint.

The resonant circuits, their manufacture and the device used for their manufacture can be modified in various ways. For example, instead of being approximately circular, the coils could easily be made in the form of a polygonal ring. Furthermore, the twisted conductor sections forming the capacitor could also be arranged on the outside of the coil instead of in the opening of the coil.

In the manufacture of the resonant circuits, one could, for example, eject the coil of a just-produced resonant circuit from the coil winding carrier 27 before the conductor is cut with the bolt-like parts 59 and 67, which would then make it possible to determine the resonant frequency of the resonant circuit after it has been ejected from the coil winding carrier 27 to measure again.

The device for the manufacture of the resonant circuits could be modified in such a way that it is provided with a frame, a workpiece carrier held rotatably about an axis of rotation and a drive device for rotating the workpiece carrier, the workpiece carrier being rotatable about a vertical axis of rotation, for example in the general round turntable can be formed. A plurality of, for example six, holding devices for holding and rotatable bearings, each distributed uniformly along the circumference of the table, can be arranged on the turntable, with the axes of rotation of the coil windings running, for example, at right angles and radially to the axis of rotation of the turntable. Various devices are arranged around the turntable on the frame and form different work stations. During operation of the device, the turntable is rotated step by step or continuously, so that the holding devices with the coil winding carriers are successively moved past the various work stations.

The device belonging to the first work station has a drive device and a winding arm which can be moved therewith, which threads the electrically insulated conductor originating from a supply coil into the coil winding carrier and then winds a predetermined number of turns of the conductor on the coil winding carrier, the latter winding around its during winding The axis of rotation is held non-rotatably and the free end of the winding arm is rotated around the coil winding support. As the turntable continues to rotate, the conductor between the supply reel and the winding wound on the coil winding support is gripped with a holding member with two grippers and cut in half with a cutting member between the two grippers. For the next step, the two ends of the conductor section wound on the coil winding support are gripped and held with a holding device which has two knife-like holding, contact and cutting elements, which first only cut through the insulation of the conductor and establish a conductive connection with it . Now a current is supplied to the conductor section wound on the coil winding carrier in order to weld the insulation of the winding. Furthermore, a drive device held on the frame is coupled to the coil winding support and the latter is rotated about its axis of rotation, as a result of which the conductor end sections protruding from the coil winding support are twisted together. The resonance frequency of the resonant circuit is measured. When the resonance frequency has reached the intended value, the twisting process is ended and the ends of the conductor are cut off with the holding, contact and cutting elements. When the coil winding carrier with the now almost finished resonant circuit arrives at the last work station, part of the coil winding carrier together with the coil is temporarily separated from the remaining part of the coil winding carrier held on the turntable and moved away. The twisted end sections of the conductor, which form the capacitor of the resonant circuit, are then rolled into the free interior of the winding of the coil using a mechanical device, so that they form an approximately circular arc there, for example. The oscillating circuit produced is then ejected onto a slide or the like using a mechanical ejector and the part of the coil winding support separated from the turntable is reconnected to the remaining part of the coil winding support. The turntable then moves the coil winding carrier back to the first work station, where the coil winding carrier is used again to produce a new resonant circuit.

With this device, different workpieces, i.e. H. resonance circuits with different levels of progress are processed in the production process. This enables fully automatic resonant circuit production with a high production rate.

However, it would also be possible to carry out some of the work steps carried out automatically in the described devices, for example by threading the insulated conductor, manually.

The holding, contacting and cutting members 53, 55 could be modified in such a way that the bolt-like parts 59 and 67 are replaced by levers which run approximately parallel to the axis of rotation 25 so as to be pivotable at right angles to the pivot axes. have cutting edges facing one end of the support 51 and a force is applied to the other end by springs corresponding to the springs 61 69.

Furthermore, one could do the different radio exerted by each of the parts 59 and 67 Assign all or part of the different elements. For example, parts 59 and '67 could primarily only be used to establish the electrical connection with the conductor and to cut it, and additional holding parts could be provided for clamping and holding the two conductor sections 11b, 11. Furthermore, the electrical connection and the cutting could be carried out by separate parts. In these cases, the cutting points should then be closer to the coil than the points at which the conductor is held and brought into electrical connection with the oscillator, so that the finished resonant circuit has no conductor sections with damaged insulation. Furthermore, in the finished resonant circuits, only relatively short, untwisted conductor sections should be present at the free ends of the conductor.

Furthermore, one could possibly modify the holding, contact and cutting elements as well as the manufacturing method in such a way that after the twisting only the twisted conductor section 11c associated with the supply of conductors is cut off. Possibly, one could insert a conductor piece cut to a predetermined length into the coil winding carrier for the production of each resonant circuit and then, after the twisting process, even completely do without cutting through conductor points.

Furthermore, there is the possibility of dimensioning the conductor sections used to form the capacitor so long and forming so many twist turns that the capacitance is certainly greater than the capacitance required to achieve the resonance frequency specified for the finished resonant circuit . The actual resonance frequency can then be measured. The cutting parts used to cut off the two conductor sections would then be adjustable along the axis of rotation 25 by an adjustment device which can be controlled by the control device 71. The control device would then have means for adjusting the cutting parts as a function of the measured resonance frequency in such a way that a part of the twisted conductor sections is also cut off from the resonant circuit, so that the finished resonant circuit then has the predetermined resonant frequency. The number of turns of the twisted conductor sections enclosing one another and thus the capacitance of the capacitor would thus also be determined in this production variant on the basis of a resonance frequency measurement.

Furthermore, it would also be possible per se to also weld the insulation sections of the conductor sections twisted together. However, when determining the frequency limit at which the twisting is terminated, it would have to be taken into account that this welding may still change the capacity.

In addition to the cut 31b, the flange 31 could also be provided with another cut so that the two conductor sections 11b, 11c to be twisted could be passed through different cuts, but the two cuts should expediently be relatively close to one another.

The different variation options mentioned can of course be combined with one another.

Claims (10)

1. Oscillatory circuit, for an article to be secured against theft, with a winding (7) formed of an insulated electrical conductor (11) and a capacitor (5) connected in parallel thereto, characterised thereby, that the capacitor (5) is formed by likewise insulated portions (11b, 11c) of the conductor (11) forming the winding (7), which portions adjoin both ends of the winding (7) and are twisted together.

2. Oscillatory circuit according to claim 1, characterised thereby, that the insulation (15) of the conductor (11) consists at least in part of a weldable thermoplastic material, in particular of a polyolefine, such as for example of polypropylene with a weldable copolymer layer or for example of polyethylene.

3. Oscillatory circuit according to claim 1 or 2, characterised thereby, that the insulation (15) of the adjacent turns of the winding (7) is welded together each time, wherein preferably all turns of the winding (7) extend along a common plane at right angles to the axis (25) of the winding (7).

4. Method for the production of a parallel oscillatory circuit, wherein a winding (7) is wound out of an insulated electrical conductor (11), characterised thereby, that portions (11b, 11 c), which adjoin both ends of the winding (7), of the conductor (11) forming the winding (7) are twisted together for the formation of a capacitor (5).

5. Method according to claim 4, characterised thereby, that for the twisting together, two portions (11b, 11c). which adjoin both ends of the winding (7), of the conductor (11) are held at holding places spaced from the winding (7) and the winding (7) is rotated about its axis (25) so that the capacitor (5) is formed between the holding places and the winding (7), wherein the holding places are preferably arranged at least approximately symmetrically to the named axis (25).

6. Method according to claim 4 or 5, characterised thereby, that the winding (7) is wound first and the named portions (11b, 11c) of the conductor (11) are twisted together thereafter, that the resonant frequency of the oscillatory circuit is measured at least during the last part of the twisting operation and/or at least after the twisting operation and that the number of mutually embracing turns of the twisted conductor portions (11b, 11c) is determined on the basis of the resonant frequency measurement.

7. Method according to one of the claims 4 to 6, characterised thereby, that the winding (7) is wound first and the named portions (11b, 11c) of the conductor (11) are twisted together thereafter, wherein the resonant frequency is measured at least during the last part of the twisting operation and named conductor portions (11 b, 11 c) are twisted together until the resonant frequency has reduced to a value which is approximately equal to a target value and/or at most equal to a limit value, wherein at least one twisted conductor portion, for example that conductor portion (11 c), which is contiguous with a supply of the conductor (11), is cut through at its end remote from the winding (7) preferably at or after the end of the twisting operation.

8. Method according to one of the claims 4 to 7, characterised thereby, that the insulation (15) of the conductor portion (11a) forming the winding (7) is welded together by heating, for example by means of an electrical current led through the conductor (11).

9. Equipment for carrying out the method according to claim 5. characterised by a frame (1). at least one rotatably borne winding carrier (27). holding means (51. 53, 55) in order after the production of a winding (7) to hold portions (11 b, 11c) of the conductor (11), which are contiguous with both ends of the winding (7), and a driving device (23) in order to rotate the winding carrier (27) and the holding means (51, 53, 55) each with respect to the other for the twisting-together of both the conductor portions (11 b, 11 c).

10. Equipment according to claim 9, characterised by a frequency meter (75), parts (59, 67) in order to bring this into electrically conductive connection with two conductor portions (11 b, 11c), which are contiguous with both the different ends of the winding (7) of an oscillatory circuit disposed in production, and means (53, 55, 73) in order to determine the number of mutually em- bracting turns of the twisted conductor portions (11 b, 11c) on the basis of the resonant frequency measurement of the oscillatory circuit disposed in production.

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