METHOD AND SYSTEM TO DETERMINE THE POSITION, ORIENTATION, SIZE, AND MOVEMENT OF RFID TAGGED OBJECTS

• US 20100328073A1
• Filed: 06/30/2009
• Published: 12/30/2010
• Est. Priority Date: 06/30/2009
• Status: Active Grant

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Rao, KVS, Ramamurthy, Shashi, Martinez, Rene, Nikitin, Pavel
• Granted Patent: US 8,248,210 B2
• Time in Patent Office: Days
• US Class Current: 340/572.1
• CPC Class Codes: G01S 5/0247 Determining attitude
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10079 the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device

Abstract

A method and system of determining spatial identification of an object, such as orientation, size, location, range, and/or movement, using an RFID system is disclosed. An RFID system can comprise one or more RFID reader receiving antennas that query one or more RFID tags coupled to the object. The measurement of the phase of the tag responses at the reader antennas and phase differentials as a function of distance, frequency, and time are the basis of spatial identification. The system can work with conventional Gen 2 tags and readers without modification of the tags or protocol.

Claims

1. A method of determining spatial information about an object coupled to one or more RFID tags using one or more receiving antennas at an RFID reader, comprising:

transmitting one or more RF inquiries to the one or more RFID tags at a first time;

measuring a phase for each RFID tag'"'"'s response at each of the one or more receiving antennas;

calculating a phase difference between the measured phases of each response for two or more tag-and-antenna pairs;

determining a first set of equations based at least on a distance formula applied between each tag-and-antenna pair distance and a corresponding phase difference;

determining a second set of equations based at least on the distance formula applied between each antenna-pair distance and known antenna spacings or between each tag-pair distance and known tag spacings; and

solving the first set of equations and the second set of equations to generate location coordinates for the one or more RFID tags.

2. The method of claim 1, further comprising:

determining a third set of equations based at least on orthogonality between antenna positional vectors if the antenna positional vectors are orthogonal or orthogonality between tag positional vectors if the tag positional vectors are orthogonal; and

solving the third set of equations with the first and second set of equations to generate location coordinates for the one or more RFID tags.

3. The method of claim 2, further comprising:

if a total number of equations in the first, second, and third sets of equations is less than three times a total number of tags, adding more equations based at least in part on measuring phase differences at one or more antennas between phases of responses from a tag to a first RF inquiry at a first frequency and a second RF inquiry at a second frequency and solving the first, second, and third sets of equations and additional equations for tag coordinates.

4. The method of claim 1 wherein the first set of equations is given by ∥

R_rm−

T_tm∥

−

∥

R_rn−

T_tn∥

=KΔ

φ

, wherein

5. The method of claim 1 wherein the second set of equations is given by ∥

R_rm−

R_rn∥

=d_rmn and ∥

T_tm−

T_tn∥

=d_tmn, wherein d_mn are the spacings between the antennas and d_tmn are the spacings between the tags, M is a first total number of antennas, N is a second total number of tags,

6. The method of claim 2 wherein the third set of equations is given by R_rm·

R_rn=0 and T_tm·

T_tn=0, wherein

7. The method of claim 1, further comprising calculating a size of the object from the tag coordinates if there are four tags located on corners of the object, and three of the tags are neighbors of a central tag.

8. The method of claim 1, further comprising calculating a linear velocity vector of the object based at least in part on transmitting one or more RF inquiries to the RFID tags at a second time, solving for tag coordinates at the second time, and dividing a difference between tag coordinates at the first time and at the second time by an elapsed time between the first time and the second time.

9. The method of claim 1, further comprising calculating a rotational velocity vector of the object based at least in part on:

calculating orientation angles of the object with respect to known antenna coordinates using the calculated tag coordinates;

transmitting one or more RF inquiries to the RFID tags at a second time;

solving for tag coordinates at the second time;

solving for orientation angles of the object with respect to known antenna coordinates at the second time; and

dividing a difference between orientation angles at the first time and at the second time by an elapsed time between the first time and the second time.

10. The method of claim 1, further comprising:

repeating and averaging the measurement of the phase at each of the one or more receiving antennas one or more times, wherein calculating the phase difference comprises calculating a difference of the averaged phase measurements; and

providing a quality of service indication based at least in part on a number of repeated phase measurements performed.

11. A method of determining spatial information about an object coupled to at least three RFID subscribers using at least one receiving antenna at an RFID interrogator, comprising:

transmitting two RFID commands from the RFID interrogator, wherein a first command is transmitted at a first frequency and a second command is transmitted at a second frequency;

receiving responses from each RFID subscriber at the receiving antenna for each RFID command;

calculating for each RFID subscriber a phase differential between the phases of that RFID subscriber'"'"'s responses at the receiving antenna;

determining a distance between each RFID subscriber and the receiving antenna based at least in part on the calculated phase differentials and a difference between the first and second frequencies;

determining one or more locations of the object using at least the determined distances and the difference between the first and second frequencies.

12. The method of claim 11, further comprising:

determining the location of the object by finding a point where three spheres intersect, wherein determining distances between each RFID subscriber and the receiving antenna establishes the three spheres that define where the object is located.

13. The method of claim 11 wherein determining the distance between each RFID subscriber and the receiving antenna is based upon a first equation

14. The method of claim 11, further comprising determining an orientation of the object by calculating relative locations of the RFID subscribers with respect to each other using a second equation Δ

d=(c/4π

f)Δ

φ

, wherein Δ

d is a subscriber distance between two subscribers, c is a speed of light, f is a transmitting frequency, and Δ

φ

is a measured phase differential at the receiving antenna between phases of responses from two subscribers.

15. The method of claim 14, further comprising determining a rotational velocity of the object by determining a change in orientation of the subscribers from the antenna over time.

16. The method of claim 11, further comprising determining a linear velocity of the object by determining a change in distance of the subscribers from the antenna over time.

17. A method of determining spatial information about an object coupled to at least one RFID tag using at least three receiving antennas at an RFID reader, comprising:

transmitting a first RF interrogation from the RFD reader at a first time;

receiving a first response from the tag at each receiving antenna;

calculating a first phase for the first response received at each receiving antenna;

calculating for each pair of antennas a first phase difference between the first phases of the received responses at the pair of antennas, wherein the each pair of antennas comprises a combination of two of the at least three receiving antennas;

determining three hyperboloids on which the tag is located based at least on the calculated first phase difference and a distance difference between the tag and each antenna of the pair of antennas;

determining first tag coordinates by finding a point where the three hyperboloids intersect.

18. The method of claim 17, further comprising:

transmitting a second RF interrogation at a second time;

receiving a second response from the tag at each receiving antenna;

calculating a second phase for each received response;

calculating for each pair of antennas a second phase difference between the second phases of the received responses at the pair of antennas;

determining three additional hyperboloids on which the tag is located at the second time based at least on the calculated second phase differences and a second distance difference between the tag and each antenna of the pair of antennas;

determining second tag coordinates by finding a second point where the three additional hyperboloids intersect

dividing a difference between the first and second tag coordinates by an elapsed time between the first time and the second time to determine a linear velocity vector of the tag.

19. The method of claim 18, further comprising:

calculating first orientation angles of the tag with respect to known antenna coordinates using the calculated first tag coordinates;

calculating second orientation angles of the object with respect to known antenna coordinates using the calculated second tag coordinates at the second time; and

dividing a difference between the first and second orientation angles by an elapsed time between the first time and the second time to determine a rotational velocity vector of the tag.

20. A method of determining spatial information about an object coupled to at least one RFID tag using at least two receiving antennas at an RFID reader, comprising:

transmitting a first RF signal at a first frequency from the RFID reader at a first time;

receiving a first response to the first RF signal from the tag at each receiving antenna;

calculating a first phase for each first response;

calculating a first phase difference between the first phases of the first responses;

determining a hyperboloid path on which the tag is located using a spatial division—

phase difference of arrival (SD-PDOA) technique based at least on the calculated first phase difference and a difference between a first distance between the tag and a first receiving antenna and a second distance between the tag and a second receiving antenna to determine a direction of the tag.

21. The method of claim 20, further comprising:

transmitting a second RF signal at a second frequency from the RFID reader, wherein the second frequency is different from the first frequency;

receiving a second response from the tag at the first receiving antenna;

calculating a second phase for the second response;

calculating a second phase difference between the first phase of the first response measured at the first receiving antenna and the second phase of the second response measured at the first receiving antenna;

determining a distance between the tag and the first receiving antenna using a FD-PDOA technique based at least in part on the calculated second phase difference and a frequency difference between the first frequency and the second frequency.

22. The method of claim 20, further comprising taking a time derivative of the determined distance to determine a linear velocity of the tag.

23. An RFID reader comprising:

one or more power supply means to power the RFID reader;

one or more input/output means to receive and provide information;

one or more transmitting antennas configured to transmit RF (radio frequency) inquiries at one or more frequencies to RFID (radio frequency identification) tags coupled to an object, wherein the RFID tags are spatially separated;

one or more transmitters coupled to the one or more transmitting antennas and configured to generate the RF inquiries to be transmitted;

one or more receiving antennas configured to receive responses to the RF inquiries from the RFID tags;

one or more receivers coupled to the one or more receiving antennas and configured to demodulate responses from the RFID tags to extract an in-phase signal and a quadrature phase signal from each response;

at least one data memory component; and

at least one processor coupled among the one or more transmitters, the one or more receivers, the switch, and the data memory component, wherein the processor is configured to;

select one or more frequencies for transmitting the RF inquiries;

calculate a phase for each response based upon the extracted in-phase signal and the quadrature phase signal;

perform one or more calculations selected from a group consisting essentially of;

calculating a distance between a first receiving antenna and a first tag using a frequency division—

phase difference of arrival (FD-PDOA) technique;

calculating a location of the object using

     1) a spatial division—

phase difference of arrival (SD-PDOA) technique with at least one tag and three receiving antennas,

     2) both the SD-PDOA and FD-PDOA techniques with at least two tags and two receiving antennas, or

     3) the FD-PDOA technique with at least three tags and one receiving antenna;

calculating an orientation of the object using the SD-PDOA technique with at least one receiving antenna and three RFID tags;

calculating a linear velocity of the object using a time division—

phase difference of arrival (TD-PDOA) technique with the calculated distance; and

calculating a rotational velocity of the object using the TD-PDOA technique with the calculated location or the calculated orientation.

24. The RFID reader of claim 23 wherein at least one of the receiving antennas is also one of the transmitting antennas, and wherein an RF switch is configured to couple at least one receiver or one transmitter to two or more of the transmitting antennas or two or more of the receiving antennas, respectively.

25. The RFID reader of claim 23 wherein the transmitting antenna and the receiving antennas are integrated into a removable fixture.

26. The RFID reader of claim 23 wherein four receiving antennas are each located on a different corner of an imaginary cube, wherein three receiving antennas are neighbors to a central receiving antenna, and the central receiving antenna also functions as the transmitting antenna.

27. The RFID reader of claim 23 wherein three receiving antennas are each located on different vertices of a substantially equilateral triangle, and the transmitting antenna is at or near a center of the triangle.

28. The RFID reader of claim 23 wherein three receiving antennas form a substantially equilateral triangle, and one of the receiving antennas also functions as the transmitting antenna.

29. The RFID reader of claim 23 wherein root-mean-square (RMS) values of the in-phase signal and quadrature phase signal are extracted from the responses;

gain and phase imbalances in the receiver are measured during calibration; and

true RMS values of the in-phase signal and quadrature phase signal are used to calculate true phases of the responses by subtracting out effects of the gain and phase imbalances.

30. The RFID reader of claim 23 wherein a distance between the receiving antennas is less than a shortest wavelength transmitted by the transmitting antenna.

31. The RFID reader of claim 23 wherein the receiver is linear and has a wide dynamic range to prevent saturation of the in-phase signal and the quadrature phase signal.

32. An RFID reader comprising:

two antennas, wherein each antenna has RF transmit and receive functionality, the two antennas are spatially separated, and the two antennas are parallel;

a transmitter configured to generate one or more RF inquiries to be transmitted to an RFID tag;

a receiver configured to receive and demodulate responses from the RFID tag;

an RF switch coupled to the two antennas, the transmitter, and the receiver, wherein the RF switch is configured to couple one of the two antennas to either the transmitter or the receiver;

at least one memory component configured to store data in the RFID reader;

at least one processor coupled among the transmitter, the receiver, the RF switch, and the data memory component, wherein the processor is configured to determine a phase for each response at each antenna to calculate an angle between a centerline of the two antennas and the RFID tag; and

at least one power supply to power the RFID reader.

33. A device for use with an RFID reader to sense a tilt of an object, comprising two or more RFID tags, wherein a first tag is positioned at a known first distance from a second tag, and further wherein the first tag is positioned at a known relative location from the second tag.

34. The device of claim 33, further comprising:

an adhesive label having a sticky surface, wherein the two or more RFD tags are coupled to the label.

35. The device of claim 33, further comprising:

a securing substrate, wherein the two or more RFID tags are secured to the substrate, and wherein the substrate includes a securing member for securing the substrate to an object.