DETECTION OF A POSITION OF AN OBJECT

• US 20130082877A1
• Filed: 08/24/2012
• Published: 04/04/2013
• Est. Priority Date: 09/29/2011
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Kamaya, Yamato, Yonezawa, Takashi, Nishi, Satoru, Tanibayashi, Makoto
• Granted Patent: US 9,128,187 B2
• Time in Patent Office: Days
• US Class Current: 342/451
• CPC Class Codes: G01S 13/874 Combination of several systems for attitude determination in general G01C, control of attitude G05D1/49
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence

Abstract

A method and associated system for estimating a position of an object. A radio wave is received from each radio frequency identification (RFID) tag of N RFID tags affixed to the object at different positions at the object (N≧2). A position of each RFID tag is detected from the received radio waves. A position of each RFID tag is estimated from analysis of the detected positions. The estimating includes utilizing, for n=1, 2, . . . , N, a specified probability function P(′p_n|p_n) denoting a probability that the estimated position of RFID tag n is p_n if the detected position of RFID tag n is p_n, wherein ′p_n and p_n are vectors from an origin of a coordinate system to the detected position and the estimated position, respectively, of the RFID tag n. The position of the object is ascertained from analysis of the estimated positions.

Claims

1. A method for estimating a position of an object, said method comprising:

receiving a radio wave from each radio frequency identification (RFID) tag of N RFID tags affixed to the object at different positions at the object, wherein N is at least 2;

detecting, from the received radio waves, a position of each RFID tag;

estimating, by a processor, a position of each RFID tag from analysis of the detected positions, wherein said estimating comprises utilizing, for n=1, 2, . . . , N, a specified probability function P(′

p_n|p_n) denoting a probability that the estimated position of RFID tag n is p_n if the detected position of RFID tag n is p_n, and wherein ′

p_n and p_n are vectors from an origin of a coordinate system to the detected position and the estimated position, respectively, of the RFID tag n; and

said processor ascertaining the position of the object from analysis of the estimated positions.

2. The method of claim 1, wherein for n=1, 2, . . . , N, ′

p_n deviates from p_n by a displacement vector S and a set A of rotational angles, and wherein said estimating the position of each RFID tag comprises utilizing the probability function P(′

p_n|p_n) to determine S and A.

3. The method of claim 2, wherein the coordinate system is a three dimensional Cartesian coordinate system having x, y, and z axes, wherein the displacement vector S has components S_x, S_y, and S_z along the x, y, and z axes, wherein the rotational angles in the set A are Eulerian angles φ

, θ

, and ψ

around respective axes of the coordinate system, and wherein said estimating the position of each RFID tag comprises determining values of S_x, S_y, S_z, φ

, θ

, and ψ

by maximizing a likelihood function L of P(′

p_n|p_n) for n=1, 2, . . . , N with respect to S_x, S_y, S_z, φ

, θ

, and ψ

.

4. The method of claim 3, wherein L=P(′

p₁|p₁)•

P(′

p₂|p₂)•

. . . •

P(′

p_N|p_N).

5. The method of claim 4, wherein ′

p_n=(p_n+S)R₁(φ

)R₂(θ

)R₃(ψ

) for n=1, 2, . . . , N, and wherein R₁(φ

), R₂(θ

), and R₃(ψ

) are respective rotation matrices for φ

, θ

, and ψ

.

6. The method of claim 5, wherein

7. The method of claim 1, wherein said ascertaining the position of the object comprises determining a reference point in the object by calculating the reference point as an average of ′

p₁, ′

p₂, . . . and ′

p_n for n=1, 2, . . . , N.

8. The method of claim 1, said method further comprising:

after said ascertaining the position of the object, transmitting the ascertained position of the object to a server device for storage of the ascertained the position of the object in a storage means of the server device.

9. The method of claim 1, said method further comprising:

before said receiving the radio wave from each RFID tag, transmitting radio signals to the N RFID tags to trigger each RFID tag to transmit the radio wave from each RFID tag that is subsequently received for said detecting the position of each RFID tag.

10. A system for estimating a position of an object, said system comprising:

means for receiving a radio wave from each radio frequency identification (RFID) tag of N RFID tags affixed to the object at different positions at the object, wherein N is at least 2;

means for detecting, from the received radio waves, a position of each RFID tag;

means for estimating a position of each RFID tag from analysis of the detected positions, wherein said estimating comprises utilizing, for n=1, 2, . . . , N, a specified probability function P(′

p_n|p_n) denoting a probability that the estimated position of RFID tag n is p_n if the detected position of RFID tag n is p_n, and wherein ′

p_n and p_n are vectors from an origin of a coordinate system to the detected position and the estimated position, respectively, of the RFID tag n; and

means for ascertaining the position of the object from analysis of the estimated positions.

11. A system comprising a receiving unit and a control unit collectively configured to perform a method for estimating a position of an object, said receiving unit coupled to the control unit, said method comprising:

said receiving unit receiving a radio wave from each radio frequency identification (RFID) tag of N RFID tags affixed to the object at different positions at the object, wherein N is at least 2;

said receiving unit detecting, from the received radio waves, a position of each RFID tag;

estimating, by a processor of the control unit, a position of each RFID tag from analysis of the detected positions, wherein said estimating comprises utilizing, for n=1, 2, . . . , N, a specified probability function P(′

p_n|p_n) denoting a probability that the estimated position of RFID tag n is p_n if the detected position of RFID tag n is p_n, and wherein ′

p_n and p_n are vectors from an origin of a coordinate system to the detected position and the estimated position, respectively, of the RFID tag n; and

said processor ascertaining the position of the object from analysis of the estimated positions.

12. The system of claim 11, wherein for n=1, 2, . . . , N, ′

p_n deviates from p_n by a displacement vector S and a set A of rotational angles, and wherein said estimating the position of each RFID tag comprises utilizing the probability function P(′

p_n|p_n) to determine S and A.

13. The system of claim 12, wherein the coordinate system is a three dimensional Cartesian coordinate system having x, y, and z axes, wherein the displacement vector S has components S_x, S_y, and S_z along the x, y, and z axes, wherein the rotational angles in the set A are Eulerian angles φ

, θ

, and ψ

around respective axes of the coordinate system, and wherein said estimating the position of each RFID tag comprises determining values of S_x, S_y, S_z, φ

, θ

, and ψ

by maximizing a likelihood function L of P(′

p_n|p_n) for n=1, 2, . . . , N with respect to S_x, S_y, S_z, φ

, θ

, and ψ

.

14. The system of claim 13, wherein L=P(′

p₁|p₁)•

P(′

p₂|p₂)•

. . . •

(′

p_N|p_N).

15. The system of claim 14, wherein ′

p_n=(p_n+S) R₁(φ

) R₂(θ

) R₃(ψ

) for n=1, 2, . . . , N, and wherein R₁(φ

), R₂(θ

), and R₃(ψ

) are respective rotation matrices for φ

, θ

, and ψ

.

16. The system of claim 15, wherein

17. The system of claim 11, wherein said ascertaining the position of the object comprises determining a reference point in the object by calculating the reference point as an average of ′

p₁, ′

p₂, . . . and ′

p_n for n=1, 2, . . . , N.

18. The system of claim 11, said method further comprising:

after said ascertaining the position of the object, said control unit transmitting the ascertained position of the object to a server device for storage of the ascertained the position of the object in a storage means of the server device.

19. The system of claim 11, said system further comprising a transmitting unit coupled to the control unit, said method further comprising:

before said receiving the radio wave from each RFID tag, said transmitting unit transmitting radio signals, under control of the control unit, to the N RFID tags to trigger each RFID tag to transmit the radio wave from each RFID tag that is subsequently received for said detecting the position of each RFID tag.

20. The system of claim 11, wherein N=8, wherein the object is a three-dimensional pallet having a shape of a rectangular solid with 8 corners, and wherein the 8 RFID tags are respectively positioned at the 8 corners of the rectangular solid.