Angle of position object location system and method

• US 7,170,412 B2
• Filed: 08/31/2004
• Issued: 01/30/2007
• Est. Priority Date: 08/31/2004
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bridgelall, Raj, Knadle, Richard T. Jr., Knox, Michael, Duron, Mark William, Bender, James Joseph
• Primary Examiner(s): TWEEL JR, JOHN ALEXANDER
• Application Number:
  US10/931,476
• Publication Number:
  US 20060044147A1
• Time in Patent Office: 882 Days
• Field of Search: 340/572.1, 340/825.49, 340/539.13, 340/572.7, 342/42, 342/44, 342/47, 342/127
• US Class Current: 340/572.1
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement
• CPC Class Codes: G01S 3/32 derived from different combinations of signals from separate antennas, e.g. comparing sum with difference
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• 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 location system and method is provided for locating objects. The system includes an RFID reader, an angle calculator, and a distance calculator to determine which of a plurality of zones an object is located in or passing through. An RFID tag is affixed with the object that is to be located. The RFID reader transmits signals to the RFID tag and receives backscatter-modulated signals from the RFID tag at one or more RFID antennas. From those received signals, the angle calculator determines an angle of position of the RFID tag relative to the RFID antenna. From the angle of position the zone in which the object is located is determined.

Claims

1. An object location system for locating an object having an RFID tag, the object location system comprising:

an RFID reader, the RFID reader transmitting a plurality of transmitted signals to the RFID tag and receiving a plurality of backscatter-modulated signals from the RFID tag; and

an angle calculator, the angle calculator determining an angle of position of the RFID tag from the backscatter-modulated signals, wherein the angle calculator determines the angle of position of the RFID tag by determining a sum of the backscatter-modulated signals received at two antennas and a difference of the backscatter modulated signals received at the two antennas, and wherein the object location system determines object location using the angle of position of the RFID tag.

2. The system of claim 1 wherein the RFID reader includes a plurality of antenna pairs, the plurality of antenna pairs positioned around a plurality of portals, wherein at least one of the plurality of antenna pairs receives the backscatter-modulated signals and wherein the angle calculator determines the angle of position of the RFID tag relative to the receiving antenna pair to determine which of the plurality of portals an object passes.

3. The system of claim 1 wherein the two antennas are coupled to a 180-degree hybrid.

4. The system of claim 1 wherein the angle calculator determines the angle of position of the RFID tag by determining a sum of the backscatter-modulated signals received at the two antennas and a difference of the backscatter-modulated signals received at the two antennas for backscatter-modulated signals from multiple locations of the object as the object moves in a known direction.

5. The system of claim 1 wherein the object location system further comprises a distance calculator, the distance calculator determining a distance from the RFID tag to the RFID reader based on the backscatter modulated signals, and wherein the object location system determines object location using both the determined distance and the angle of position.

6. The system of claim 5 wherein the distance calculator determines a distance from the RFID tag to the RFID reader by determining a rate of change of the phase in a plurality of backscatter-modulated signals with respect to rate of change in a fundamental frequency of a plurality of transmitted signals.

7. The system of claim 6 wherein the rate of change of the phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency of the plurality of transmitted signals is determined by performing a linear trend fit of the phase in the plurality of backscatter-modulated signals versus the fundamental frequency of the plurality of transmitted signals.

8. An object location system for locating an object having an RFID tag, the object moving along a path, the object location system comprising:

an RFID transmitter, the RFID transmitter transmitting a plurality of transmitted signals to the RFID tag as the object moves along the path;

a plurality of RFID antenna pairs, at least one of the plurality of RFID antenna pairs receiving a plurality of backscatter modulated signal from the RFID tag in response to the plurality of transmitted signals as the object moves along multiple locations along the path;

an angle calculator, the angle calculator determining an angle of position of the RFID tag relative to at least one of the plurality of RFID antenna pairs, wherein the angle calculator determines the angle of position of the RFID tag by determining a vector sum of the backscatter-modulated signal received at the at least one of the plurality of RFID antenna pairs and by determining a vector delta of the backscatter-modulated signal received at the at least one of the plurality of RFID antenna pairs for the plurality of backscatter-modulated signals from the RFID tag at the multiple locations of the object as the object moves along the path.

9. The system of claim 8 wherein each of the RFID antenna pairs comprises a 180 degree hybrid.

10. The system of claim 8 wherein the angle calculator determines the angle of position by determining a rotation direction of the vector sum and vector delta in sum-delta space resulting from the multiple backscatter-modulated signals from the RFID tag at multiple locations of the object as the object moves along the path.

11. The system of claim 10 wherein a rotation in the sum-delta space in a first direction corresponds to an angle of position of less than 90 degrees and wherein a rotation in the sum-delta space in a second direction corresponds to an angle of position of between 180 degrees and 90 degrees.

12. The system of claim 11 wherein the RFID transmitter transmits the plurality of transmitted signals at a rate selected to cause a rotation in the sum-delta space of less than 90 degrees between consecutive transmissions.

13. The system of claim 8 wherein the system is configured to determine which of a plurality of portals the object is passing through.

14. The system of claim 8 further comprising a distance calculator, the distance calculator determining a distance from the RFID tag to the at least one of the plurality of RFID antenna pairs based on a phase difference in the backscatter modulated signals, and wherein the object location system determines object location using both the determined distance and the angle of position of the RFID tag.

15. The system of claim 14 wherein the distance calculator determines a distance from the RFID tag to the RFID reader by determining a rate of change of the phase in a plurality of backscatter-modulated signals with respect to rate of change in a fundamental frequency of a plurality of transmitted signals, and wherein the rate of change of the phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency of the plurality of transmitted signals is determined by performing a linear trend fit of the phase in the plurality of backscatter-modulated signals versus the fundamental frequency of the plurality of transmitted signals.

16. The system of claim 14 wherein the RFID reader continues to transmit additional transmitted signals and receive additional backscatter-modulated signals and wherein the distance calculator continues to determine a phase for each of the additional backscatter-modulated signals received and uses the phase for each additional backscatter-modulated signal to determine the distance from the RFID reader to the RFID tag is until the distance is computed within a specified level of accuracy.

17. A method of locating an object having an RFID tag, the method comprising the steps of:

transmitting a plurality of transmitted signals from an RFID reader to the RFID tag;

receiving a plurality of backscatter-modulated signals from the RFID tag;

determining an angle of position of the RFID tag from the backscatter-modulated signals, wherein the step of determining an angle of position of the RFID tag from the backscatter-modulated signals comprises determining a sum of the backscatter-modulated signals received at two antennas and a difference of the backscatter modulated signals received at the two antennas; and

determining an object location using the angle of position of the RFID tag.

18. The method of claim 17 wherein the step of receiving a plurality of backscatter-modulated signals from the RFID tag comprises receiving at least one pair of antennas in a plurality of pairs of antennas, and wherein the step of determining an angle of position of the RFID tag from the backscatter-modulated signals comprises determining the angle of position of the RFID tag relative to the at least one pair of antennas.

19. The method of claim 17 wherein the determining a sum of the backscatter-modulated signals received at the two antennas and a difference of the backscatter modulated signals received at the two antennas are performed by a 180-degree hybrid.

20. The method of claim 17 wherein the step of determining an angle of position of the RFID tag from the backscatter-modulated signals comprises determining a sum of the backscatter-modulated signals received at the two antennas and a difference of the backscatter-modulated signals received at the two antennas for backscatter-backscatter modulate signals from multiple locations of the object as the object moves is a known direction.

21. The method of claim 17 further comprising the step of determining a distance from the RFID tag to the RFID reader based on the backscatter-modulated signals, and wherein the step of determining an object location using the angle of position of the RFID tag comprises using the determined distance and the angle of position.

22. The method of claim 21 wherein the step of computing a distance to the RFID tag comprises determining a rate of change of phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency of the plurality of transmitted signals.

23. The method of claim 22 wherein the step of computing a distance to the RFID tag by determining a rate of change of phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency comprises performing a linear trend fit of the phase in the plurality of backscatter-modulated signals versus the fundamental frequency of the plurality of transmitted signals.

24. A method of locating an object having an RFID tag moving along a path, the method comprising the steps of:

transmitting a plurality of transmitted signals from an RFID reader to the RFID tag as the object moves along the path;

receiving a plurality of backscatter-modulated signals from the RFID tag at at least one of a plurality of RFID antenna pairs as the object moves along multiple locations along the path;

determining a vector sum of the backscatter-modulated signal received at the at least one of the plurality of RFID antenna pairs and determining a vector delta of the backscatter-modulated signal received at the at least one of the plurality of RFID antenna pairs for the plurality of backscatter-modulated signals from the RFID tag as the object moves along the multiple locations;

determining an angle of position of the RFID tag from the vector sum and vector delta; and

determining an object location using the angle of position of the RFID tag.

25. The method of claim 24 wherein each of the RFID antenna pairs comprises a 180-degree hybrid.

26. The method of claim 24 wherein the step of determining an angle of position of the RFID tag from the vector sum and vector delta comprises determining a rotation direction of the vector sum and vector delta in sum-delta space resulting from the multiple backscatter-modulated signals from the RFID tag at multiple locations of the object as the object moves along the path.

27. The method of claim 26 wherein a rotation in the sum-delta space in a first direction corresponds to an angle of position of less than 90 degrees and wherein a rotation in the sum-delta space in a second direction corresponds to an angle of position of between 180 degrees and 90 degrees.

28. The method of claim 27 wherein the step of transmitting a plurality of transmitted signals from an RFID reader to the RFID tag as the object moves along the path comprises transmitting signals at a rate selected to cause a rotation in the sum-delta space of less than 90 degrees between consecutive transmissions.

29. The method of claim 24 wherein the step of determining an object location using the angle of position of the RFID tag comprises determining which of a plurality of portals the object is passing through.

30. The method of claim 24 further comprising the step of determining a distance from the RFID tag to the RFID reader based on the backscatter-modulated signals, and wherein the step of determining an object location using the angle of position of the RFID tag comprises using the determined distance and the angle of position.

31. The method of claim 30 wherein the step of computing a distance to the RFID tag comprises determining a rate of change of phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency of the plurality of transmitted signals by performing a linear trend fit of the phase in the plurality of backscatter-modulated signals versus the fundamental frequency of the plurality of transmitted signals.

32. The method of claim 31 wherein the step of computing a distance to the RFID tag by determining a rate of change of phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency comprises continuing to continues to transmit additional transmitted signals and receive additional backscatter-modulated signals until the distance is computed within a specified level of accuracy.