Method and apparatus for sensitizing and desensitizing targets for electronic article surveillance systems

• US 5,225,807 A
• Filed: 09/16/1991
• Issued: 07/06/1993
• Est. Priority Date: 09/16/1991
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: Knogo Corp (Johnson Controls International plc)
• Inventors: Zhou, Peter Y., Pang, Dexing
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): MULLEN, THOMAS J
• Application Number:
  US07/760,506
• Time in Patent Office: 659 Days
• Field of Search: 340/551, 340/572, 335/284, 310/152, 310/154, 310/156
• US Class Current: 340/572.3
• CPC Class Codes: G08B 13/2411 Tag deactivation

Abstract

Magnetically desensitized targets or sensor elements on protected articles are resensitized by means of rotating permanent magnets which are moved relative to the magnetized target desensitizer elements such that the elements become subjected to reversing magnetic fields of gradually decreasing intensity.

Claims

1. A sensitizer for sensitizing electronic surveillance system targets of the type that have a plurality of spaced apart magnetizable elements along their length, said sensitizer comprising a base, a motor mounted in said base, a carrier mounted in said base for rotation about a given axis and connected to be rotated by said motor, and at least one permanent magnet mounted on said carrier at a location and orientation such that upon rotation of said carrier, the poles of said magnet revolve around said given axis and the magnetic field from said magnet extends out from said base and means for positioning a target to be sensitized such that magnetized elements extending along the length thereof become successively exposed to cyclically reversing magnetic fields.

2. A sensitizer according to claim 1, wherein said means for positioning a target comprises a sensitizer wall having a surface mounted at a fixed position relative to said axis.

3. A sensitizer according to claim 1, and further including a brake for holding said carrier at a predetermined fixed rotational position about said given axis whereby said sensitizer is converted to operate as a target desensitizer.

4. A sensitizer according to claim 3, wherein said brake comprises an element located at a fixed position relative to said given axis and arranged to produce a magnetic interaction with said permanent magnet which is greatest at said predetermined fixed rotational position.

5. A sensitizer according to claim 1, wherein a plurality of magnets are arranged on said carrier with polar axes parallel to each other and perpendicular to and intersecting said given axis.

6. A sensitizer according to claim 1, wherein said carrier comprises a cylindrically shaped element of non-magnetic material mounted with its longitudinal axis extending along said given axis for rotation about said given axis and wherein said permanent magnet extends through said carrier with the polar axis of said permanent magnet intersecting and extending perpendicular to said given axis.

7. A sensitizer according to claim 6, wherein a plurality of permanent magnets extend through said carrier with their polar axes parallel to each other.

8. A sensitizer according to claim 7, wherein said permanent magnets are closely spaced to each other with their respective North poles close to each other and their South poles close to each other to produce a band of magnetic flux extending around the outer surface of said carrier.

9. A sensitizer according to claim 1, wherein said motor, carrier and magnet are mounted in a housing and wherein said housing includes a sensitizer wall for positioning an article containing a target to be sensitized, said sensitizer wall being closely spaced to a plane defined by the poles of said magnet as they revolve around said given axis.

10. A sensitizer according to claim 9, wherein said sensitizer wall extends in a flat plane.

11. A sensitizer according to claim 10, wherein said housing includes a guide wall at a substantially right angle to said sensitizer wall and intersecting said sensitizer wall along a line which extends in a direction substantially perpendicular to the direction of said given axis.

12. A sensitizer according to claim 1, wherein said means for positioning a target comprises a handle attached to said carrier.

13. A sensitizer according to claim 12, wherein said permanent magnet is oriented with its polar axis perpendicular to said given axis.

14. A sensitizer according to claim 13, wherein the polar axis of said permanent magnet intersects said given axis.

15. A sensitizer according to claim 14, wherein said carrier comprises a cylindrical element whose longitudinal axis extends along said given axis and wherein said permanent magnet is embedded in said cylindrical element.

16. A sensitizer according to claim 12, wherein said motor and said carrier are enclosed within a common housing and wherein said handle is attached to and forms part of said common housing.

17. A sensitizer according to claim 16, wherein said motor is enclosed within said handle and wherein a portion of said housing which contains said carrier extends beyond said handle.

18. A sensitizer according to claim 17, wherein said common housing supports a battery for supply of electrical power to said motor.

19. A sensitizer according to claim 1, wherein said motor and said carrier are driveably connected by a drive belt.

20. A method of sensitizing electronic surveillance system targets of the type that have a plurality of spaced apart magnetizable elements along their length, said method comprising the steps of causing the poles of at least one permanent magnet to revolve around a given axis to produce, in a given region, a cyclically reversing magnetic field and causing a desensitized target to enter into and exit from said reversing magnetic field.