Body motion tracking system

• US 6,784,826 B2
• Filed: 01/26/2001
• Issued: 08/31/2004
• Est. Priority Date: 01/26/2001
• Status: Expired due to Fees

• Current Assignee: Tera Research, Inc. (Alion Science & Technology Corp.)
• Original Assignee: Tera Research, Inc. (Alion Science & Technology Corp.)
• Inventors: Spain, David Stevenson Jr., Kane, Ronald J.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/770,237
• Publication Number:
  US 20020145563A1
• Time in Patent Office: 1,313 Days
• Field of Search: 342/118, 342/127, 342/417-449, 342/27, 342/28, 342/42, 342/43-51, 342/56, 342/142, 342/151, 342/175, 342/195, 342/450-465, 340/540, 340/541, 340/552-567, 340/573.1, 340/574, 340/575, 340/576, 340/573.2, 340/573.3, 340/573.4, 340/573.7
• US Class Current: 342/28
• CPC Class Codes: A61B 5/1038 Measuring plantar pressure during gait
• CPC Class Codes: G01S 2205/09 for tracking people
• CPC Class Codes: G01S 5/0294 Trajectory determination or predictive filtering, e.g. target tracking or Kalman filtering
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

Methods and apparatus are disclosed for measuring position and motion of a “marker” antenna (14), disposed on a subject (12) at a physical location to be tracked. Relative distance of the marker antenna (14) from receiving antennas (18) is measured by phase differences of its microwave signals (40) at the receiving antennas (18) for at least two successive marker positions. Alternatively, actual distances (104, 106) are calculated by choosing a source position (102) and iterating the distances (104, 106) until the calculated phase differences match those measured. Four to six receiving antennas (18) are positioned at edges of a volume (16) where activity is conducted. Each received signal (40) is amplified and down-converted in a mixer (44). A single reference oscillator (46) feeds all the mixers (42) to preserve phase relationships of the received signals. Received signals (40) are digitized and presented to a multi-channel digital tuner (50). Phase relationships are preserved because all of the signal processing up to this step is “coherent”. The digital data is fed (51) to a main computer and processed by algorithm to estimate the marker antenna'"'"'s position relative to each receiving antenna (18). The apparatus is especially applicable to clinical gait analysis, sports medicine, industrial, military and entertainment uses.

Claims

1. A method for capturing the position and movement of a subject living body comprising the steps of:

providing a transmitter (73);

said transmitter (73) disposed on a subject (12) at a location to be tracked;

said subject (12) moving from position-to-position within a volume of space (16);

emitting a signal (40) from transmitter (73);

providing a plurality of widely-spaced receiving antennas (76, 78) disposed at edges of said volume of space (16);

measuring a phase difference (Δ

φ

1) of said signal (40) being received at each independent pair of said plurality of receiving antennas (76, 78) when said transmitter (73) is at a first position (72);

changing a physical position of said transmitter (73) from a first position (72) to a second position (74);

measuring a phase difference (Δ

φ

2) of said signal (40) being received at each said independent pair of said plurality of receiving antennas (76, 78) when said transmitter (73) is at a second position (74); and

estimating a change in said physical position of said transmitter (73) by comparing measured phase differences (Δ

φ

1, Δ

 

2) of received said signal (40) at each said independent pair of said plurality of receiving antennas (76,78).

2. The method as claimed in claim 1, in which the step of providing a transmitter (73) disposed on a subject (12) includes the step of providing a low-power radio frequency transmitter (30) coupled to a marker antenna (14) on said subject (12).

3. The method as claimed in claim 2, in which the step of emitting a signal (40) from said transmitter (73) includes emitting a microwave signal (40) from said marker antenna (14).

4. The method as claimed in claim 3, in which said plurality of receiving antennas (76, 78) includes at least four receiving antennas.

5. The method as claimed in claim 1, in which the step of estimating a change in said physical position (72, 74) of said transmitter (73) by comparing measured phase differences (Δ

φ

) of received said signal (40) at each one of said plurality of receiving antennas (76, 78) further includes the steps of;

measuring a signal phase (φ

) at each one said widely spaced plurality of receiving antennas (76, 78) when said subject living body (12) is at a first position;

moving said transmitter (73) with said subject living body (12) from said first position (72) a distance (82) to said second position (74);

measuring a change of said received signal phase (Δ

φ

) at each of said widely spaced plurality of receiving antennas (76, 78) when said energy source is at said second position (74);

estimating the direction of motion and the distance 82 moved by comparing said measured change of received signal phase (Δ

φ

) at said widely-spaced plurality of receiving antennas (76, 78);

said received signal phase (φ

) being dependent only on a signal wave length (λ

) and said distance and direction moved (82) by said transmitter (73); and

continuing said movement (82) and repeating said signal phase measurements, thereby tracking the direction and motion of said transmitter (73) without use of an absolute phase reference.

6. The method as claimed in claim 1, in which the step of estimating a change in said physical position (72, 74) of said transmitter (73) by comparing measured phase differences (Δ

φ

) of received said signal (40) at each one of said plurality of receiving antennas (76,78) further includes the steps of;

measuring a signal phase difference (Δ

φ

) of received said signal (40) at each one of said widely spaced plurality of receiving antennas (76,78);

evaluating all allowable values of a difference of pairs (Δ

n) of integer values (n1, n2) which give the same said measured value of said signal phase difference (Δ

φ

);

selecting a set of said values of a difference of pairs (Δ

n) of integer values (n1, n2) for which surfaces of all hyperbolas of revolution which are defined by said difference of pairs (Δ

n) of integer values (n1, n2) intersect at a same point; and

said same point of intersection being said physical position (74) of said transmitter (73) at the time of said signal phase difference (Δ

φ

) measurement.

7. The method as claimed in claim 6, in which said microwave signal is at a frequency of approximately 2.4 GHz.

8. The method as claimed in claim 7, adapted to mapping of human muscle, joint and bone interactions for performing clinical gait analysis of persons having neuromuscular, musculoskeletal, or neurological impairments.

9. The method as claimed in claim 7, adapted to mapping and analysis of human body motion for improving performance in sports.

10. The method as claimed in claim 7, adapted to mapping human body motion for evaluation of human interaction with military equipment.

11. The method as claimed in claim 7, adapted to tracking body motion of humans and animals for implementing realistic animation in film and television entertainment.

12. The method as claimed in claim 7, adapted to tracking body motion of humans and animals for implementing realistic animation in computer games and presentations.

13. An apparatus for capturing the position and movement of a subject living body comprising the steps of:

a transmitter (73);

said (73) disposed on a subject (12) at a location to be trucked;

said subject (12) moving from position-to-position within a volume of space (16);

said transmitter source (73) emitting a signal (40);

a plurality of widely-spaced receiving antennas (76, 78), each one of said plurality of receiving antennas (76, 78) being disposed at edges of said volume of space (16);

a phase difference (Δ

φ

1), of said emitted signal (40) being measured at each independent pair of said plurality of receiving antennas (76, 78) when said transmitter energy-source (73) is at a first position (72);

a phase difference (Δ

φ

2), of said emitted signal (40) being measured at said independent pair of said plurality of receiving antennas (76, 78) after moving said transmitter (73) from a first position (72) to a second position (74);

end

a change (82) in said physical position (72, 74) of said transmitter source (73) being determined by comparing a change in said measured phase difference (Δ

φ

2-Δ

φ

1) of received said signal (40) at each said independent pair of said plurality of receiving antennas (76, 78).

14. The apparatus as claimed in claim 13, in which said transmitter (73) disposed on a subject (12) includes a low-power radio frequency transmitter (30) coupled to a marker antenna (14).

15. The apparatus as claimed in claim 14, in which said emitted signal (40) from said transmitter (73) includes a microwave signal (40) from said marker antenna (14).

16. The apparatus as claimed in claim 15, in which said microwave signal is at a frequency of approximately 2.5 GHz.

17. The apparatus as claimed in claim 15, in which said plurality of receiving antennas includes at least four receiving antennas.

18. The apparatus as claimed in claim 13, in which:

the direction of motion and the distance moved (82) by said transmitter (73) being dependent only on a signal wave length (λ

) and a change of relative phase of the received, propagated signal (40); and

said measurements being repeated as said movement (82) continues, thereby tracking the direction and motion of said transmitter (73) without use of an absolute phase reference.

19. A method A method for capturing the position and movement of a subject living body comprising the steps of:

providing a transmitter (102);

disposing said transmitter (102) on a subject (12) at a location to be tracked;

said subject (12) moving from position-to-position within a volume of space (16);

emitting a signal (40) having a wavelength (λ

) from said transmitter (102);

providing a plurality of widely-spaced receiving antennas (108, 110) disposed at edges of said volume of space (16);

representing a length (d) of each signal path (104, 106) from said transmitter (102) to each one of said plurality of widely-spaced receiving antennas (108, 110) as an integer number (n) of said signal wavelengths (λ

) plus a fractional signal wavelength (δ

);

a difference in signal path length (Δ

d) to each one of any pair of said plurality of widely-spaced receiving antennas (108, 110) being characterized by a difference of said integer numbers (n1-n2) multiplied by said signal wavelength (λ

) plus a difference in said fractional signal wavelengths (δ

1-δ

2);

assuming a plurality of values of integer number difference (Δ

n), a first said integer number difference (Δ

n1) being characterized as a first integer value (n1) less a second integer value (n2), a second said integer number difference (Δ

n2) being characterized as a third integer value (n3) less a fourth integer value (n4) and so on, for each value of integer number difference (Δ

n) possible within said volume of space (16);

measuring a phase difference (Δ

φ

) between each said signal (40) received from said transmitter (102) at each said pair of said plurality of receiving antennas (108, 110);

each one of said plurality of values of integer number difference (Δ

n) and each said measured phase difference (Δ

φ

) defining a surface of locations (112) upon which said transmitter (102) may be located;

selecting one of said plurality of values of integer difference (Δ

n) for each pair of said plurality of receiving antennas (108, 110) and calculating a potential location (103) having a smallest mean square distance from all of the surfaces of location (112) defined by said selected values of integer difference (Δ

n) and said measured phase differences (Δ

φ

);

iterating said calculations of said potential energy source location using all of said assumed plurality of values of integer difference (Δ

n) possible within said volume of space (16) and finding each said position (103) until a final absolute energy-source position (103) is found at which a smallest said mean square distance from corresponding said surfaces of location (112) exists.

20. The method as claimed in claim 19, in which the step of providing a plurality of widely-spaced receiving antennas (108, 110) disposed at edges of said volume of space (16), includes providing at least four widely-spaced receiving antennas.

21. The apparatus as claimed in claim 19, in which said transmitting means (73) includes a low-power, radio frequency transmitter (30) coupled to a marker antenna (14).

22. The apparatus as claimed in claim 21, which said emitted signal (40) from said transmitter (73) includes a microwave signal (40) emitted from said marker antenna (14).

23. The apparatus as claimed in claim 22, in which said microwave signal is at a frequency of approximately 2.5 GHz.

24. The apparatus as claimed in claim 22, adapted to mapping of human muscle, joint and bone interactions for performing clinical gait analysis of persons having neuromuscular, musculoskeletal, or neurological impairments.

25. The apparatus as claimed in claim 22, adapted to mapping and analysis of human body motion for improving performance in sports.

26. The apparatus as claimed in claim 22, adapted to mapping human body motion for evaluation of human interaction with military equipment.

27. The apparatus as claimed in claim 22, adapted to tracking body motion of humans and animals for implementing realistic animation in film and television entertainment.