Use of rotating magnetic field to enhance communication with RF burst-transmitting tags of object location system

• US 6,812,839 B1
• Filed: 03/27/2001
• Issued: 11/02/2004
• Est. Priority Date: 03/27/2000
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Belcher, Donald K., Hash, Ronald J.
• Primary Examiner(s): TWEEL JR, JOHN ALEXANDER
• Application Number:
  US09/818,276
• Publication Number:
  US 20040203361A1
• Time in Patent Office: 1,316 Days
• Field of Search: 340/572.1, 340/572.2, 340/572.3, 340/572.4, 340/505, 340/573.1, 340/551, 340/572.7
• US Class Current: 340/572.1
• 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

Magnetic field-based communication with an object is enhanced by generating a rotating AC magnetic field that effectively ensures magnetic field coupling with the magnetic field sensor of the object, irrespective of the orientation of the object. The rotating AC magnetic field is produced by a diverse spatial orientation (a two-dimensional arrangement) of a plurality of magnetic field coils, and the driving of those coils in a prescribed phase relationship (e.g., in phase quadrature) to realize a composite AC magnetic field that rotates (at the carrier frequency of the coil drive signal) over the entirety of the spatial coverage area.

Claims

1. A method of communicating with objects whose locations are monitored on a continuous basis using RF transmissions from tags associated with the objects within an asset management environment having a plurality of tag transmission readers geographically distributed within and/or around the asset management environment, at least one area in the asset management environment being an area of increased sensitivity region prone to orientation null problems for receiving tag emissions, wherein outputs of said tag transmission readers are coupled to an object location processor which processes outputs of said tag transmission readers to locate said tags and thereby their associated objects within said monitored environment comprising the steps of:

(a) generating an AC magnetic field that rotates over a region of increased sensitivity into which an object may enter and which is representative of information intended for said object entering said region; and

(b) at said object entering said region of increased sensitivity detecting said rotating AC magnetic field.

2. A method according to claim 1, wherein said step (a) comprises generating a plurality of respectively spatially and phase offset AC magnetic fields that form within said region a composite AC magnetic field that rotates over said region.

3. A method according to claim 1, wherein step (a) comprises providing a distribution of spatially offset magnetic field generators proximate to said region, and causing said distribution of spatially offset magnetic field generators to generate said phase offset AC magnetic fields and thereby form within said region said composite AC magnetic field that rotates over said region, and spatially provides complete magnetic field coverage for said region irrespective of the orientation of said object.

4. A method according to claim 3, wherein said region comprises a passageway connecting separate portions of, or has mobility within, said monitored environment.

5. A method according to claim 1, wherein step (a) comprises frequency shift key encoding said rotating AC magnetic field in accordance with information intended for said object.

6. A method according to claim 1, wherein said rotating AC magnetic field is a non-modulated AC magnetic field.

7. A method according to claim 1, wherein step (a) comprises providing, proximate to said region, a plurality of AC magnetic field generators having a multi-dimensional arrangement of output field coils, axes of which are non-parallel with one another, that are adapted to be driven with phase offset AC drive signals and thereby produce said composite AC magnetic field that rotates over said region at the frequency of said AC drive signals.

8. An arrangement for communicating with an object whose locations are monitored on a continuous basis using RF transmissions from tags associated with the objects entering a region of increased sensitivity within an asset management environment having a plurality of tag transmission readers geographically distributed within and/or around the asset management environment, at least one area in the asset management environment being an area of increased sensitivity region prone to orientation null problems for receiving tag emissions, wherein outputs of said tag transmission readers are coupled to an object location processor which processes outputs of said tag transmission readers to locate said tags and thereby their associated objects within said monitored environment comprising:

a plurality of AC magnetic field generators at each region of increased sensitivity and having a multi-dimensional arrangement of output field coils, axes of which are proximate said region and non-parallel with one another, and which are adapted to be driven with phase offset AC drive signals and thereby produce a composite AC magnetic field that rotates over said region at the frequency of said AC drive signals; and

a magnetic field receiver installed on said object and being operative, in response to detecting said rotating AC magnetic field, to cause said object to perform a prescribed function.

9. An arrangement according to claim 8, wherein said magnetic field generators are operative to frequency shift key encode said rotating AC magnetic field in accordance with information intended for said object.

10. An arrangement according to claim 8, wherein said plurality of AC magnetic field generators are operative to generate non-modulated AC magnetic fields.

11. For use with a system for communicating with an object within a monitored environment, wherein an RF transmission from a tag associated with said object is detected at one of a plurality of monitoring locations containing a tag transmission reader, and an output of said tag transmission reader is processed to identify said object within said monitored environment, an arrangement for controlling the operation of a tag that comes within a prescribed proximity of prescribed region of increased sensitivity within said monitored environment, said arrangement comprising:

a plurality of AC magnetic field generators at said region of increased sensitivity and having a multi-dimensional arrangement of output field coils, axes of which are proximate said region and non-parallel with one another, and which are adapted to be driven with respective phase offset AC drive signals and thereby produce a composite AC magnetic field that rotates over said region at the frequency of said AC drive signals; and

a magnetic field receiver with said object and being operative to detect said rotating AC magnetic field.

12. An arrangement according to claim 11, wherein said magnetic field generators are operative to frequency shift key encode said rotating AC magnetic field in accordance with information intended for said object.

13. An arrangement according to claim 11, wherein said plurality of AC magnetic field generators are operative to generate non-modulated AC magnetic fields.