Optimization of the field profile on a high field strength magnetic detacher

• US 8,054,185 B2
• Filed: 04/07/2009
• Issued: 11/08/2011
• Est. Priority Date: 12/17/2008
• Status: Active Grant

• Current Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Original Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Inventors: Ho, Wing K., Johnson, William III, Davis, Ronald Joseph, Lian, Ming-Ren
• Primary Examiner(s): LEE, BENJAMIN C
• Application Number:
  US12/419,623
• Publication Number:
  US 20100148969A1
• Time in Patent Office: 945 Days
• Field of Search: 340/572.9, 3405721-5728, 70/571, 243/03, 335/306
• US Class Current: 340/572.9
• CPC Class Codes: E05B 73/0017 Anti-theft devices, e.g. tags or monitors, fixed to articles, e.g. clothes, and to be removed at the check-out of shops
• CPC Class Codes: E05B 73/0052 of the magnetic type
• CPC Class Codes: H01F 7/0273 Magnetic circuits with PM for magnetic field generation

Abstract

A magnetic detacher has a core magnet and a ring magnet. The core magnet has a body with a top and bottom surface, and produces a first magnetic field. The ring magnet defines a cavity. The ring magnet has a body with a top and bottom and produces a second magnetic field. The ring magnet is axially aligned with the core magnet such that the first magnetic field opposes the second magnetic field along the bodies and enhances it within the cavity. The top surface of the core magnet is separated from the bottom surface of the ring magnet by a predetermined distance thereby producing a resultant magnetic field having a first resultant field strength at a specific position greater than a second resultant field strength produced at the same position when the top surface of the core magnet abuts the bottom surface of the ring magnet.

Claims

1. A magnetic detacher comprising:

a housing defining an inner volume;

a core magnet positioned within the inner volume, the core magnet having a body with a top surface and a bottom surface opposite the top surface, the core magnet producing a first magnetic field; and

a ring magnet positioned within the inner volume, a ring magnet defining a cavity having a first diameter, the ring magnet having a body with a top surface and a bottom surface opposite the top surface, the ring magnet producing a second magnetic field and axially aligned with the core magnet such that the first magnetic field opposes the second magnetic field within the bodies of the respective magnets and enhances the second magnetic field within the cavity, the top surface of the core magnet separated from the bottom surface of the ring magnet by a predetermined distance to produce a resultant magnetic field having a first resultant field strength at a specific position greater than a second resultant field strength produced at the same position when the top surface of the core magnet abuts the bottom surface of the ring magnet.

2. The magnetic detacher of claim 1, further comprising a spacer having a height equal to the predetermined distance, the spacer positioned between the top surface of the core magnet and the bottom surface of the ring magnet.

3. The magnetic detacher of claim 2, wherein the spacer is constructed from one of non-ferromagnetic material, plastic and cloth.

4. The magnetic detacher of claim 3, further comprising a shield element, the shield element positioned proximate to the top surface of the ring magnet such that the shield element reduces a stray magnetic field outside the magnetic detacher.

5. The magnetic detacher of claim 4, wherein the shield element defines a first footprint and the ring magnet defines a second footprint, the first footprint being substantially the same as the second footprint.

6. The magnetic electronic article surveillance tag detacher of claim 4, wherein the shield element has a thickness of less than 1 mm.

7. The magnetic detacher of claim 3, further comprising a booster element, the booster element constructed of ferromagnetic material and positioned proximate to the top surface of the ring magnet such that the resultant magnetic field is enhanced.

8. The magnetic detacher of claim 1, wherein the electronic article surveillance tag detacher operates to nest a magnetic securing device for detachment, the magnetic securing device having a protrusion, the diameter of the cavity being greater than an outer diameter of the protrusion such that the cavity operates to receive the protrusion during detachment.

9. The magnetic detacher of claim 8, wherein the magnetic securing device includes a clutch mechanism, a location of the clutch mechanism substantially coinciding with the specific position when the magnetic securing device is nested in the magnetic electronic article surveillance tag detacher.

10. A magnet assembly for use in a magnetic detacher comprising, the magnet assembly comprising:

a core magnet having a body with a top surface and a bottom surface opposite the top surface, the core magnet producing a first magnetic field; and

a ring magnet defining a cavity having a first diameter, the ring magnet having a body with a top surface and a bottom surface opposite the top surface, the ring magnet producing a second magnetic field and axially aligned with the core magnet such that the first magnetic field opposes the second magnetic field along the bodies of the respective magnets and enhances the second magnetic field within the cavity, the top surface of the core magnet separated from the bottom surface of the ring magnet by a predetermined distance thereby producing a resultant magnetic field having a first resultant field strength at a specific position greater than a second resultant field strength produced at the same position when the top surface of the core magnet abuts the bottom surface of the ring magnet.

11. The magnet assembly of claim 10, further comprising a spacer having a height equal to the predetermined distance, the spacer positioned between the top surface of the core magnet and the bottom surface of the ring magnet.

12. The magnet assembly of claim 11, wherein the spacer is constructed from one of plastic and cloth.

13. The magnet assembly of claim 10, wherein the magnetic detacher operates to nest a magnetic securing device for detachment, the magnetic securing device having a protrusion, the diameter of the cavity being greater than an outer diameter of the protrusion such that the cavity operates to receive the protrusion during detachment.

14. The magnet assembly of claim 13, wherein the magnetic securing device includes a clutch mechanism, a location of the clutch mechanism substantially coinciding with the specific position when the magnetic securing device is nested in the magnetic detacher.

15. The magnet assembly of claim 10, further comprising a shield having a height equal to the predetermined distance, the shield positioned between the top surface of the core magnet and the bottom surface of the ring magnet such that the shield reduces a stray magnetic field outside the magnetic detacher.

16. The magnet assembly of claim 15 wherein the shield defines a first footprint and the ring magnet defines a second footprint, the first footprint being substantially the same as the second footprint.

17. The magnet assembly of claim 15, wherein the shield element has a thickness less than 1 mm.

18. A method for detaching a magnetic securing device from an item, the magnetic securing device secured by a clutch mechanism engaging a magnetic locking mechanism, the method comprising:

receiving the magnetic securing device in a magnetic detacher, the magnetic detacher including;

a core magnet having a body with a top surface and a bottom surface opposite the top surface, the core magnet producing a first magnetic field; and

a ring magnet defining a cavity having a first diameter, the ring magnet having a body with a top surface and a bottom surface opposite the top surface, the ring magnet producing a second magnetic field and axially aligned with the core magnet such that the first magnetic field opposes the second magnetic field along the bodies of the respective magnets and enhances the second magnetic field within the cavity, the top surface of the core magnet separated from the bottom surface of the ring magnet by a predetermined distance thereby producing a resultant magnetic field having a first resultant field strength at a specific position greater than a second resultant field strength produced at the same position when the top surface of the core magnet abuts the bottom surface of the ring magnet; and

using the field strength at the specific position to disengage the clutch mechanism to release the magnetic locking mechanism.

19. The method of claim 18, wherein the magnetic detacher further includes a spacer having a height equal to the predetermined distance, the spacer positioned between the top surface of the core magnet and the bottom surface of the ring magnet.

20. The method of claim 18, wherein the magnetic securing device defines a protrusion, the diameter of the cavity being greater than an outer diameter of the protrusion such that the cavity operates to receive the protrusion during detachment.