Electronic article surveillance marker

Abstract

A fabrication process produces markers for a magnetomechanical electronic article surveillance system. The marker includes a magnetomechanical element comprising one or more resonator strips of magnetostrictive amorphous metal alloy; a housing having a cavity sized and shaped to accommodate the resonator strips for free mechanical vibration therewithin; and a bias magnet to magnetically bias the magnetomechanical element. The process employs adaptive control of the cut length of the resonator strips, correction of the length being based on the deviation of the actual marker resonant frequency from a preselected, target marker frequency. Use of adaptive, feedback control advantageously results in a much tighter distribution of actual resonant frequencies. Also provided is a web-fed press for continuously producing such markers with adaptive control of the resonator strip length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages will become apparent when reference is had to the following detailed description of the preferred embodiments of the invention and the accompanying drawing, wherein like reference numerals denote similar elements throughout the several views, and in which:

FIG. 1 is an exploded, perspective view of a prior art EAS marker;

FIG. 2 is an exploded, perspective view of an EAS marker in accordance with the invention;

FIG. 3 is an end-on, cross-sectional view of the EAS marker of FIG. 3;

FIG. 4 is a plan view of one form of an EAS marker cavity of the invention;

FIG. 5 is a schematic diagram in side elevation view of a process for continuously manufacturing magnetomechanical EAS markers in accordance with the invention;

FIG. 6 is a broken, plan view of a portion of a web of markers during production in accordance with the invention; and

FIGS. 7A and 7B are schematic diagrams in side elevation view and bottom plan view, respectively, of a detection system used in production of EAS markers in accordance with the invention.

Claims

1. A process for fabricating a sequence of magnetomechanical EAS markers, each marker having a marker resonant frequency substantially equal to a preselected target resonant frequency, the process comprising: a. providing a plurality of housings for said markers, each housing having therein a cavity adapted to contain a magnetomechanical element consisting essentially of at least one resonator strip;b. cutting elongated resonator strips sequentially from a supply of magnetostrictive amorphous metal alloy, each of said resonator strips having a resonator strip cut length;c. installing at least one of said resonator strips in each of said cavities to provide said magnetomechanical element;d. associating a bias element with each of said housings;e. activating each of said markers by magnetizing said bias element, whereby said marker is armed to resonate at said marker resonant frequency;f. measuring said marker resonant frequency of each of the markers in a preselected sample portion of said sequence;g. adaptively controlling said resonator strip cut length for resonator strips incorporated in subsequently produced markers of said sequence, said cut length being adjusted to an updated resonator strip cut length determined from a difference between said measured marker resonant frequencies of said sample portion and said target resonant frequency, whereby said difference for said subsequently produced markers is reduced; andh. repeating steps (f) and (g) during the course of said fabrication.

2. A process as recited by claim 1, wherein said magnetomechanical element comprises a plurality of strips.

3. A process as recited by claim 2, wherein said magnetomechanical element consists essentially of two of said strips in stacked registration.

4. A process as recited by claim 1, wherein said magnetostrictive amorphous metal alloy is unannealed.

5. A process as recited by claim 1, wherein said magnetostrictive amorphous metal alloy consists essentially of an FeNiMoB-containing alloy.

6. A process as recited by claim 1, wherein said magnetostrictive amorphous metal alloy is annealed.

7. A process as recited by claim 1, wherein said bias element comprises at least one bias strip of a semi-hard magnetic material, said bias strip having a bias strip shape and bias strip dimensions.

8. A process as recited by claim 1, wherein said sample portion comprises substantially all the markers within an interval of said sequence.

9. A process as recited by claim 8, wherein said updated resonator strip cut length is determined from an average of said measured marker resonant frequencies of said markers of said sample portion.

10. A process as recited by claim 9, wherein said average is a weighted, moving average.

11. A process as recited by claim 9, wherein said sample portion comprises a number of markers ranging from about 10 to 1000.

12. A process as recited by claim 11, wherein said sample portion comprises is a number of markers ranging from about 50 to 500.

13. A process as recited by claim 9, wherein said adjustment is inversely proportional to said difference between said measured marker resonant frequency average and said target resonant frequency.

14. A process for fabricating a sequence of magnetomechanical EAS markers, each marker having a marker resonant frequency substantially equal to a preselected target resonant frequency, the process comprising: a. forming a plurality of cavities along a web of cavity stock, each of said cavities having a substantially rectangular, prismatic shape open on a large side and a lip extending around the periphery of said opening of said cavity;b. cutting elongated resonator strips sequentially from a supply of magnetostrictive amorphous metal alloy, said resonator strips having substantially the same resonator strip cut length;c. installing at least one of said resonator strips in each of said cavities to provide a magnetomechanical element;d. affixing a planar lid to said lips to close said cavity and contain said magnetomechanical element therewithin;e. cutting bias strips from a supply of semi-hard magnetic material, said bias strips having a bias shape and substantially the same dimensions;f. fixedly disposing one of said bias strips on said planar lid in registration with said magnetomechanical element;g. activating said markers by magnetizing said bias strips, whereby said markers are armed to resonate at said marker resonant frequency;h. measuring said marker resonant frequency of each of the markers in a preselected sample portion of said sequence;i. adaptively controlling said resonator strip cut length for resonator strips incorporated in subsequently produced markers of said sequence, said cut length being adjusted to an updated resonator strip cut length determined from a difference between said measured marker resonant frequency and said target resonant frequency, whereby said difference for said subsequently produced markers is reduced;j. repeating steps (h) and (i) through the course of said fabrication; andk. cutting said web to separate said markers.

15. A process as recited by claim 14, wherein said resonator strips are unannealed.

16. A process as recited by claim 14, wherein said magnetomechanical element comprises a plurality of said strips.

17. A process as recited by claim 14, wherein said cut markers are adhered to a release liner.

18. A process as recited by claim 14, wherein said magnetomechanical element consists essentially of two of said strips in stacked registration.

19. A process as recited by claim 14, wherein said cut markers are adhered to a release liner.

20. A press for fabricating a sequence of magnetomechanical EAS markers, each marker having a marker resonant frequency, the press comprising: a. a web infeed system for delivering a continuous web of cavity stock;b. a cavity formation die for forming a plurality of cavities along said web, each of said cavities having a substantially rectangular, prismatic shape open on a large side and side walls surrounding the cavity and defining a periphery;c. a resonator cutter for cutting elongated resonator strips sequentially from a supply of magnetostrictive amorphous metal alloy to an adjustable, preselected resonator strip cut length and installing at least one of said sequentially cut strips in each of said cavities to provide a magnetomechanical element;d. an affixing system for affixing a planar lid to said periphery to close said cavity and contain said magnetomechanical element therewithin; ande. a bias strip cutter for cutting bias strips from a supply of semi-hard magnetic material, and fixedly disposing one of said bias strips on said planar lid in registration with said magnetomechanical element, said bias strips having a bias shape and substantially the same dimensions.

21. A press as recited by claim 20, wherein said periphery is formed by a lip atop said cavity side walls and said lid is affixed to said lip.

22. A press as recited by claim 20, wherein said resonator cutter is adapted to install a plurality of said sequentially cut strips in stacked registration in each of said cavities.

23. A press as recited by claim 20, further comprising an activation magnet system comprising at least one magnet for activating said markers by magnetizing said bias strips, whereby said markers are armed to resonate at said marker resonant frequency.

24. A press as recited by claim 23, further comprising a control system for adaptively adjusting said resonator strip length during fabrication of said sequence to match said marker resonant frequency to a target resonant frequency, the control system comprising: a. a measurement system comprising a transmitter for imposing a burst of electromagnetic field having substantially said target resonant frequency onto a preselected sample portion of markers of said sequence, said burst exciting said markers of said sample portion sequentially into magnetomechanical resonance, and a receiver for detecting said marker resonant frequency during a ringdown after said burst; andb. a computing system connected to said receiver and said resonator cutter, said computing system recording said marker resonant frequency for said markers of said sample portion, computing an updated resonator strip cut length based on a difference between said recorded resonant frequencies and said target resonant frequency, and causing adjustment of said resonator strip cut length to said updated resonator strip cut length for subsequently cut resonator strips to reduce said difference for subsequent markers of said sequence.

25. A press as recited by claim 23, wherein said sample portion comprises substantially all the markers within an interval of said sequence.

26. A press as recited by claim 23, wherein said adjustment is based on an average of measured marker resonant frequencies of said sample portion.

27. A press as recited by claim 23, wherein said adjustment is inversely proportional to said difference.

28. For use in an apparatus for fabricating a sequence of magnetomechanical EAS markers to a preselected target resonant frequency, each marker comprising: (i) a magnetomechanical element comprising at least one elongated resonator strip having a resonator strip cut length; (ii) a housing having a cavity sized and shaped to accommodate said strip and permit it to mechanically vibrate freely therewithin; and (iii) a bias magnet magnetically biasing said magnetomechanical element, whereby said magnetomechanical element is armed to resonate at a marker resonant frequency in the presence of an interrogating electromagnetic field; an in-line frequency measurement system for measuring said marker resonant frequency of markers of said sequence during said fabrication and an adaptive control system for adjusting said resonant strip cut length during said fabrication for resonator strips incorporated in subsequently produced markers of said sequence, said adjustment being based on a difference between said measured marker resonant frequency and said target resonant frequency, whereby said difference for said subsequently produced markers is reduced.

29. For use in an electronic article surveillance system, a magnetomechanical marker that exhibits magnetomechanical resonance at a marker resonant frequency in response to the incidence thereon of an electromagnetic interrogating field, the marker comprising: a. a housing having a cavity sized and shaped to accommodate a magnetomechanical element;b. a magnetomechanical element comprising at least two elongated resonator strips composed of unannealed magnetostrictive amorphous metal alloy and having substantially the same dimensions and disposed in said cavity in stacked registration and able to mechanically vibrate freely therewithin; andc. a bias magnet adapted to be magnetized to magnetically bias said magnetomechanical element, whereby said magnetomechanical element is armed to resonate at said marker resonant frequency in the presence of an electromagnetic interrogating field.

30. A marker as recited by claim 29, said bias magnet being magnetized.

31. A marker as recited by claim 29, said bias magnet consisting essentially of a semi-hard magnetic material.

32. A marker as recited by claim 29, said magnetostrictive amorphous metal alloy consisting essentially of an FeNiMoB-containing alloy.

33. In an electronic article surveillance system having a magnetomechanical marker that exhibits magnetomechanical resonance at a marker resonant frequency, whereby the marker is provided with a signal-identifying characteristic; an interrogating means for generating an electromagnetic interrogating field having a preselected interrogating frequency; a detecting means for detecting the signal-identifying characteristic; and an indication means activated by the detecting means in response to the detection of the signal-identifying characteristic, the improvement wherein the marker comprises: a. a magnetomechanical element comprising at least two elongated, substantially planar resonator strips composed of unannealed magnetostrictive amorphous metal alloy and having substantially the same dimensions;b. a housing having a cavity sized and shaped to accommodate said resonator strips, and said resonator strips being disposed in said cavity in stacked registration and able to mechanically vibrate freely therewithin; andc. a bias magnet magnetically biasing said magnetomechanical element, whereby said magnetomechanical element is armed to resonate at said marker resonant frequency in the presence of said electromagnetic interrogating field and provided with said signal identifying characteristic.

34. A system as recited by claim 33, wherein said preselected interrogating frequency is modulated as a series of pulses and said marker resonates at said resonant frequency and radiates a marker dipole field in response to incidence of said interrogating field; and said signal-identifying characteristic is a ring-down of said dipole field.