Method and apparatus for automatically desensitizing sensor elements of protected articles

• US 5,500,640 A
• Filed: 04/25/1995
• Issued: 03/19/1996
• Est. Priority Date: 11/04/1993
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: Knogo North America, Inc. (Sentry Technology Corp.)
• Inventors: Pang, Dexing, Paul, Christopher R., Zhou, Peter Y.
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): WONG, ALBERT KANG
• Application Number:
  US08/429,229
• Time in Patent Office: 329 Days
• Field of Search: 340/572, 340/551, 364/419.17, 335/284, 235/384, 235/400, 235/499, 235/500
• US Class Current: 335/284
• CPC Class Codes: G08B 13/2411 Tag deactivation
• CPC Class Codes: G08B 13/248 EAS system combined with another detection technology, e.g. dual EAS and video or other presence detection system

Abstract

A desensitizer apparatus for desensitizing a security sensor element in a book spine. The apparatus includes a scanner which scans along a surface against which book spines are positioned and which detects sensor elements in the spines to be sure that only one book is positioned against the surface. If only one sensor element is detected, a signal is generated which operates a drive mechanism to move desensitizer magnets close to the surface to deactivate the sensor element in the book.

Claims

1. Apparatus for desensitizing sensor elements which are mounted on protected articles, said apparatus comprising:

a sensor element detector;

a scanning mechanism which moves said detector to produce a scan along a surface adjacent to which multiple sensor elements may be placed, the movement of the detector being in a direction such that, during said scan, said detector passes directly over each of said sensor elements in succession and successively detects the presence of each of said sensor elements;

a sensor element desensitizing mechanism arranged to be operated to desensitize said sensor elements adjacent said surface; and

a control apparatus connected to operate the desensitizing mechanism following a scan in response to the detection of a predetermined number of sensor elements during said scan.

2. Apparatus according to claim 1, wherein said articles are books, each of which has at least one of said sensor elements mounted in the spine thereof and wherein said predetermined number is one.

3. Apparatus according to claim 2, wherein said surface is formed on a vertical wall against one side of which said books may be placed, and along the other side of which said scanner is arranged to scan.

4. Apparatus according to claim 3, wherein said desensitizing mechanism is arranged to move toward and away from said other side of said wall.

5. Apparatus according to claim 3, wherein said scanner comprises a sensor which is responsive to the presence of a sensor element in proximity thereto to produce a detection signal.

6. Apparatus according to claim 5, wherein said scanner comprises an oscillator whose oscillation amplitude is affected by the presence of a sensor element in proximity thereto.

7. Apparatus according to claim 6, wherein said oscillator includes an elongated coil which is maintained parallel to and adjacent said wall, and extends in a direction transverse to the direction of scan, said coil being connected to form a portion of a resonant tank circuit of said oscillator whose resonant frequency corresponds to the inductance of said coil.

8. Apparatus according to claim 7, wherein a ferrite core extends through said coil.

9. Apparatus according to claim 4, wherein said desensitizing mechanism includes magnetizing elements for magnetizing desensitizing elements on a sensor element positioned in proximity thereto.

10. Apparatus according to claim 5, wherein said control apparatus includes a counter for counting detection signals from said scanner during one scan.

11. Apparatus according to claim 6, wherein said control apparatus is operative to count detection signals only during a scan in a single direction.

21. Apparatus according to claim 6, wherein said sensor is a coil whose inductance is changed by relative movement toward and away from a sensor element.

12. A method of desensitizing sensor elements which are mounted on protected articles, said method comprising the steps of:

positioning articles on which sensor elements are mounted such that said sensor elements are arranged along a scanning surface;

moving a sensor element detector along said surface to produce a scan such that said detector passes, in succession, directly over each of said sensor elements and successively detects the presence of said sensor elements; and

, following such scan, desensitizing said sensor elements in response to detection of a predetermined number of sensor elements during said scan.

13. A method according to claim 12, wherein said articles are books, each of which has one of said sensor elements mounted in the spine thereof and wherein said predetermined number is one.

14. A method according to claim 13, wherein said scanning is carried out along one side of a vertical wall, against the other side of which said books are placed.

15. A method according to claim 14, wherein said desensitizing is carried out by moving a desensitizing mechanism toward and away from said one side of said wall.

16. A method according to claim 14, wherein said sensor element detector produces, during said scanning, a detection signal as said detector moves along said wall and passes by one of said sensor elements.

17. A method according to claim 16, wherein said scanning is carried out by causing an oscillator, whose oscillation amplitude is affected by the presence of one of said sensor elements in proximity thereto, to move along said wall.

18. A method according to claim 17, wherein said desensitizing is carried out by producing magnetic fields of sufficient strength to magnetize desensitizing elements on sensor elements adjacent said wall.

19. A method according to claim 18, wherein detection signals produced by said sensor element detector are counted during a scan in one direction, to ascertain whether one, or more than one, protected article has been positioned against said surface.

20. A method according to claim 19, wherein said desensitizing is carried out only in response to the occurrence of one detection signal during a scan in one direction along said wall.

22. A method according to claim 16, wherein the electrical reactance of said sensor element detector is changed by the presence of a sensor element to thereby produce a signal.