Proximity-based magnetic field generator for controlling operation of RF burst-transmitting tags of geolocation system

• US 6,853,687 B2
• Filed: 01/11/2001
• Issued: 02/08/2005
• Est. Priority Date: 01/12/2000
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Belcher, Donald K., Hash, Ronald J., Harrington, Timothy C.
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US09/759,290
• Publication Number:
  US 20020077710A1
• Time in Patent Office: 1,489 Days
• Field of Search: 375/259, 375/272, 340/825.36, 340/525, 340/539, 340/572.1, 340/551, 700/13, 342/126, 342/450
• US Class Current: 375/259
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00

Abstract

An object tracking system for locating radio-tagged objects within a monitored environment has a plurality tag transmission readers that detect RF transmissions from the tags, and generate output signals representative of the time-of-arrival of first-to-arrive tag transmissions. An object location processor processes the first to arrive signals in accordance with a multilateration algorithm to geolocate a tag. In order to modify the operation of a tag that comes within a prescribed region of the monitored environment (such as passing through a doorway), one or more relatively short range, magnetic field proximity-based, tag-programming ‘pingers’, are placed proximate to the region. A magnetic field receiver on the tag detects the field generated by the pinger and causes the tag to change operation such as increase its RF transmission rate.

Claims

1. A method of controlling the operation of a system for geolocating objects within a monitored environment, wherein RF transmissions from tags associated with said objects are detected at a plurality of spaced apart monitoring locations containing tag transmission readers, and outputs of said tag transmission readers are coupled to an object location processor which processes outputs of said tag transmissions to geolocate said tags and thereby their associated objects within said monitored environment, said method comprising the steps of:

(a) generating, from at least location of the monitored environment that is proximate to a region which a tagged object may enter, a magnetic field encoded with information intended for a tag entering said region; and

(b) at a tag that has entered said region, detecting said magnetic field and causing said tag to perform a prescribed function.

2. A method according to claim 1, wherein step (b) comprises causing said tag to change the repetition rate of RF transmissions therefrom.

3. A method according to claim 1, wherein step (b) comprises causing said tag to increase the repetition rate of RF transmissions therefrom while said tag is proximate to said region, and thereafter causing said tag to revert to its previous repetition rate after said tag is no longer proximate to said region.

4. A method according to claim 1, wherein step (a) comprises providing a distribution of magnetic field generators proximate to said region, and causing said distribution of magnetic field generators to generate a plurality of magnetic fields encoded with said information and which provide complete spatial coverage for said region irrespective of the orientation of said tag.

5. A method according to claim 4, wherein said region comprises a passageway connecting separate portions of, or has mobility within, said monitored environment.

6. A method according to claim 1, wherein step (a) comprises frequency shift key encoding said magnetic field in accordance with said information.

7. A method according to claim 1, wherein said magnetic field is capable of penetrating media that block radio signals.

8. An arrangement for controlling the operation of a system for geolocating objects within a monitored environment, wherein RF transmissions from tags associated with said objects are detected at a plurality of spaced apart monitoring locations containing tag transmission readers, and outputs of said tag transmission readers are coupled to an object location processor, which processes said outputs of said tag transmissions to geolocate said tags and thereby their associated objects within said monitored environment, said arrangement comprising:

at least one magnetic field generator located proximate to a region which a tagged object may enter, and being operative to generate a magnetic field encoded with information intended for a tag entering said region; and

a magnetic field receiver installed on said tag and being coupled with RF transmission circuitry of said tag, and being operative, in response to detecting said magnetic field, to cause said tag to perform a prescribed function.

9. An arrangement according to claim 8, wherein said magnetic field receiver is operative to cause said tag to change the repetition rate of RF transmissions therefrom.

10. An arrangement according to claim 8, wherein said magnetic field receiver is operative to cause said tag to increase the repetition rate of RF transmissions therefrom while said tag is proximate to said region, and to cause said tag to revert to its previous repetition rate after said tag is no longer proximate to said region.

11. An arrangement according to claim 8, wherein said at least one magnetic field generator comprises a distribution of magnetic field generators proximate to said region, which are operative to generate a plurality of magnetic fields encoded with said information and provide complete spatial coverage for said region irrespective of the orientation of said tag.

12. An arrangement according to claim 9, wherein said region comprises a passageway connecting separate portions of, or has mobility within, said monitored environment.

13. An arrangement according to claim 9, wherein said at least one magnetic field generator is operative to frequency shift key encode a magnetic field generated thereby in accordance with said information.

14. An arrangement according to claim 9, wherein said magnetic field is capable of penetrating media that block radio signals.

15. An arrangement according to claim 9, wherein said magnetic field generator is capable of programming said tag.

16. An arrangement according to claim 9, wherein said magnetic field generator is configured to selectively address multiple tags or individual tags located proximate to said region.

17. For use with a system for geolocating objects within a monitored environment, wherein RF transmissions from tags associated with said objects are detected at a plurality of spaced apart monitoring locations containing tag transmission readers, and outputs of said tag transmission readers are coupled to an object location processor, which processes said outputs of said tag transmissions to geolocate said tags and thereby their associated objects within said monitored environment, an arrangement for controlling the operation of a tag that comes within a prescribed proximity of prescribed region of said monitored environment, said arrangement comprising:

at least one magnetic field generator located proximate to said region and being operative to generate at least one magnetic field modulated with information used to control the operation of said tag; and

a magnetic field receiver installed on said tag and being coupled with RF transmission circuitry of said tag, and being operative, in response to detecting information modulated on said at least one magnetic field by said at least one magnetic field generator, to cause said tag to increase the rate of RF transmissions thereby.

18. An arrangement according to claim 17, wherein said at least one magnetic field generator comprises a distribution of magnetic field generators proximate to said region, which are operative to generate a plurality of limited range magnetic fields encoded with said information and arranged to provide complete magnetic field spatial coverage for said region irrespective of the orientation of said tag.

19. An arrangement according to claim 18, wherein said region comprises one of a passageway connecting separate portions of or has mobility within said monitored environment.

20. An arrangement according to claim 18, wherein said at least one magnetic field generator is operative to frequency shift key encode at least one magnetic field generated thereby in accordance with said information.