Method and apparatus for deactivating magnetic targets

• US 5,126,720 A
• Filed: 01/17/1991
• Issued: 06/30/1992
• Est. Priority Date: 01/17/1991
• Status: Expired due to Term

• Current Assignee: Knogo North America, Inc. (Sentry Technology Corp.)
• Original Assignee: Knogo Corp (Johnson Controls International plc)
• Inventors: Solaski, Thomas P., Zhou, Peter Y., Pang, Dexing
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Oda, Christine K.
• Application Number:
  US07/642,359
• Time in Patent Office: 530 Days
• Field of Search: 340/551, 340/572, 335/306
• US Class Current: 335/284
• CPC Class Codes: G08B 13/2411 Tag deactivation

Abstract

Articles of merchandise (42) which contain deactivatable theft detection targets (44) have their targets deactivated by passing them through a box-like apparatus (30) made of low coercive force, high saturation induction material with a multiplicity of permament magnets (48) on its inside surfaces so as to generate magnetic fields which extend at different directions and at decreasing intensities from one end of the apparatus to the other so that irrespective of a target'"'"'s orientation while passing through the apparatus, the target'"'"'s magnetic deactivation slugs or elements will encounter a magnetizing field along the target'"'"'s length sufficient to magnetize the elements.

Claims

1. A method for deactivating randomly oriented elongated magnetic targets having elongated magnetizable slugs distributed along their length, said method comprising the steps of successively subjecting the slugs of each target to magnetic fields of successively reduced intensity which extend in different directions, each of said magnetic fields being of sufficient intensity to magnetize the slugs along a target sufficiently to deactivate the target when the direction of the field is substantially the same as that of the target.

2. The method according to claim 1 wherein said magnetic fields are distributed along a given path and said targets are moved along said path.

3. The method according to claim 1 or 2 wherein said magnetic fields extend in substantially all directions.

4. A method according to claim 3 wherein the intensity and direction of each magnetic field is maintained substantially constant during target deactivation.

5. An apparatus for deactivating randomly oriented elongated magnetic targets having elongated magnetizable slugs distributed along their length, said apparatus comprising means for producing magnetic fields which extend in different directions and means for successively subjecting the slugs on each target to a different one of said fields, each of said magnetic fields being of sufficient intensity to magnetize the slugs along a target sufficiently to deactivate the target when the direction of the field is substantially the same as that of the target, said means for producing said magnetic fields being constructed and arranged to generate fields of successively reduced intensity along a given path.

6. The apparatus according to claim 5 wherein said means for producing magnetic fields is constructed and arranged to produce fields which extend at said different directions at successive locations along said path, and along which path said targets may be moved.

7. The apparatus according to claim 5 or 6 wherein said means for producing magnetic fields is constructed and arranged to produce fields which extend in substantially all directions.

8. The apparatus according to claim 7 wherein said means for producing magnetic fields is constructed and arranged to maintain the intensity and direction of each magnetic field substantially constant during target deactivation.

9. The apparatus according to claim 7 wherein said means for producing magnetic fields comprises a plurality of spaced apart permanent magnets.

10. Apparatus according to claim 9 wherein said permanent magnets are mounted on a wall of low coercive force, high saturation induction material yoke.

11. Apparatus according to claim 9 wherein said apparatus comprises a yoke made up of walls of low coercive force, high saturation induction material and wherein said magnets are spaced apart on each of said walls.