Motion tracking system

• US 6,176,837 B1
• Filed: 04/17/1998
• Issued: 01/23/2001
• Est. Priority Date: 04/17/1998
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Foxlin, Eric M.
• Primary Examiner(s): O'Connor, Cary
• Assistant Examiner(s): MARMOR II, CHARLES ALAN
• Application Number:
  US09/062,442
• Time in Patent Office: 1,012 Days
• Field of Search: 600/587, 600/595, 364/478.01, 348/169, 367/117, 367/118, 128/898, 128/897, 73/488, 73/503.3, 73/504.03, 73/510, 73/514.01
• US Class Current: 600/595
• CPC Class Codes: A61B 5/1038 Measuring plantar pressure during gait
• CPC Class Codes: G01C 21/1652 with ranging devices, e.g. LIDAR or RADAR
• CPC Class Codes: G01S 11/16 using difference in transit time between electrical and acoustic signals
• CPC Class Codes: G01S 15/86 Combinations of sonar systems with lidar systems; Combinations of sonar systems with systems not using wave reflection
• CPC Class Codes: G01S 15/87 Combinations of sonar systems
• CPC Class Codes: G01S 5/186 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49

Abstract

Tracking a motion of a body by obtaining two types of measurements associated with the motion of the body, one of the types including acoustic measurement. An estimate of either an orientation or a position of the body is updated based on one of the two types of measurement, for example based on inertial measurement. The estimate is then updated based on the other of the two types of measurements, for example based on acoustic ranging. The invention also features determining range measurement to selected reference devices that are fixed in the environment of the body.

Claims

1. A method for tracking a motion of a body comprising:

obtaining three types of measurements associated with the motion of the body, a first type comprising acoustic measurement, a second type comprising linear inertial measurement, and a third type comprising angular inertial measurement;

updating an estimate of a position of the body based on the second type of measurement;

updating the position estimate based on the first type of measurement; and

updating an estimate of an orientation of the body based on the third type of measurement.

2. The method of claim 1 in which the first type of measurement comprises acoustic ranging.

3. The method of claim 1 in which the estimate of orientation is undated based on the first type of measurement.

4. An apparatus for tracking motion of a body comprising:

three sensor systems configured respectively to obtain three types of measurements associated with motion of the body, a first type comprising acoustic measurement, a second type comprising linear inertial measurement and a third type comprising angular inertial measurement; and

a processor coupled to the three sensor systems and configured to update an estimate of a position of the body based on the second type of measurement, to update the position estimate based on the the first type of measurement, and to update an estimate of an orientation of the body based on the third type of measurement.

5. A tracking device comprising:

a sensor system including

an inertial sensor; and

a set of one or more acoustic sensors rigidly coupled to the inertial sensor; and

a processor programmed to perform the functions of

accepting inertial measurements from the inertial sensor;

updating a location estimate and an orientation estimate of the sensor system using the accepted inertial measurements;

selecting one of a plurality of acoustic reference devices;

accepting an acoustic range measurement related to the distance between the sensor system and the selected acoustic reference device;

updating the location estimate and the orientation estimate using the accepted range measurement.

6. The tracking device of claim 5 wherein the sensor system includes a transmitter for transmitting a control signal encoding an identifier of the selected acoustic reference device, and each acoustic sensor includes a microphone for receiving an acoustic signal from the acoustic reference device.

7. The tracking device of claim 5, wherein the set of one or more acoustic sensors includes two or more acoustic sensors.

8. The tracking device of claim 5, wherein the processor is configured to

update a location estimate and an orientation estimate using the accepted inertial measurements by updating an uncertainty in the location and the orientation estimates; and

update the location estimate and the orientation estimate using the accepted range measurement by determining an uncertainty in the range measurement and updating the uncertainty in the location and the orientation estimates using the uncertainty in the range measurement.

9. A method for tracking the motion of a body including:

selecting one of a plurality of reference devices;

transmitting a control signal to the selected reference device;

receiving a range measurement signal from the reference device;

accepting a range measurement related to a distance to the selected reference device; and

updating a location estimate or an orientation estimate of the body using the accepted range measurement.

10. The method of claim 9, further comprising:

determining a range measurement based on a time of flight of the range measurement signal.

11. The method of claim 10 further comprising:

determining a range measurement based on a time of flight of the range measurement signal.

12. The method of claim 10 wherein transmitting the control signal includes transmitting a wireless control signal.

13. Software stored on a computer readable medium comprising instructions for causing a computer to perform the functions of:

selecting one of a plurality of reference devices;

transmitting a control signal to the selected reference device;

receiving a range measurement signal from the reference device;

accepting a range measurement related to a distance to the selected reference device; and

updating a location estimate or an orientation estimate of the body using the accepted range measurement.

14. A tracking system comprising:

an acoustic reference system including a plurality of acoustic reference devices; and

a tracking device including

a sensor system including an inertial sensor and a set of one or more acoustic sensors rigidly coupled to the inertial sensor, and

a processor programmed to perform the functions of accepting inertial measurements from the inertial sensor, updating a location estimate and an orientation estimate of the sensor system using the accepted inertial measurements, selecting one of a plurality of acoustic reference devices, accepting an acoustic range measurement related to the distance between the sensor system and the selected acoustic reference device, and updating the location estimate and the orientation estimate using the accepted range measurement.

15. The system of claim 14 wherein the sensor system includes a transmitter for transmitting a control signal encoding an identifier of the selected acoustic reference device, and each acoustic sensor includes a microphone for receiving an acoustic signal from the acoustic reference device, and wherein each acoustic reference device includes a receiver for receiving the control signal from the sensor system, and an acoustic transducer for sending the acoustic signal.

16. The system of claim 14, further comprising more than three acoustic receivers.

17. An apparatus for tracking motion of a body comprising:

two sensor systems configured respectively to obtain two types of measurements associated with motion of the body, one of the types comprising acoustic measurement, wherein the sensor system for obtaining acoustic measurement comprises greater than three acoustic receivers; and

a processor coupled to the two sensor systems and configured to update an estimate of either an orientation or a position of the body based on one of the two types of measurement, and to update the estimate based on the other of the two types of measurement.

18. The apparatus of claim 17, wherein one of the types of measurement comprises acoustic ranging.

19. The apparatus of claim 17, in which the other of the types of measurement comprises inertial measurement.

20. The apparatus of claim 17 in which the processor is configured to update an estimate of orientation based on the first type of measurement.

21. The apparatus of claim 20 in which the processor is configured to update an estimate of position based on the first type of measurement.

22. A method for tracking the motion of a body including:

selecting one of a plurality of reference devices;

transmitting a control signal to the selected reference device;

accepting a range measurement related to a distance to the selected reference device; and

updating a location estimate or an orientation estimate of the body using the accepted range measurement.

23. The method of claim 22, further comprising:

receiving a range measurement signal from the selected reference device; and

determining a range measurement based on a time of flight of the range measurement signal.

24. The method of claim 22, wherein transmitting the control signal includes transmitting a wireless control signal.

25. Software stored on a computer readable medium comprising instructions for causing a computer to perform the functions of:

selecting one of a plurality of reference devices;

transmitting a control signal to the selected reference device;

accepting a range measurement related to a distance to the selected reference device; and

updating a location estimate or an orientation estimate of the body using the accepted range measurement.

26. A tracking device comprising:

a sensor system including

an inertial sensor; and

a set of one or more acoustic sensors rigidly coupled to the inertial sensor; and

a processor programmed to perform the functions of accepting inertial measurements from the inertial sensor;

updating a location or orientation estimate of the sensor system using the accepted inertial measurements;

selecting one of a plurality of acoustic reference devices;

accepting an acoustic range measurement related to the distance between the sensor system and the selected acoustic reference device;

updating the estimate using the accepted range measurement.

27. The tracking device of claim 26, wherein the sensor system includes a transmitter for transmitting a control signal encoding an identifier of the selected acoustic reference device, and each acoustic sensor includes a microphone for receiving an acoustic signal from the selected acoustic reference device.

28. The tracking device of claim 26, wherein the set of one or more acoustic sensors includes two or more acoustic sensors.

29. The tracking device of claim 26, wherein the set of one or more acoustic sensors includes more than three acoustic sensors.

30. The tracking device of claim 26, wherein

the processor is configured to

update the estimate using the accepted inertial measurements by updating an uncertainty in the estimate; and

update the estimate using the accepted range measurement by determining an uncertainty in the range measurement and updating the uncertainty in the estimate using the uncertainty in the range measurement.

31. A tracking system for tracking the position of a body comprising:

a sensor system comprising a plurality of acoustic receivers rigidly coupled to a portable assembly; and

a plurality of acoustic reference devices arrayed at a distance from the portable assembly, wherein the acoustic receivers are arrayed on the portable assembly so that at least one of the acoustic receivers is positioned to receive signals from at least three of the acoustic reference devices regardless of the orientation of the portable assembly.

32. The tracking system of claim 31, wherein the plurality of acoustic receivers comprises greater than 3 receivers.

33. The system of claim 32, further comprising a processor programmed to select, based on the current orientation of the portable assembly, a subset of the acoustic receivers according to their ability to receive signals from the acoustic reference devices.

34. The tracking system of claim 31, wherein for a majority of the orientations of the portable assembly, at least two of the acoustic receivers are positioned to receive signals from at least three of the acoustic reference devices.

35. A method for tracking motion of a rigid body comprising:

disposing a plurality of transducers in the environment;

mounting a plurality of transducers on the body;

measuring the range between a selected one of the transducers disposed in the environment and a selected one of the transducers mounted on the body;

predicting a range measurement between the selected transducer in the environment and the selected transducers mounted on the body;

updating an estimate of the orientation or position of the body based on the difference between the actual range measurement and the predicted range measurement.

36. The method of claim 35, wherein the transducers disposed in the environment are acoustic emitters and the transducers mounted on the body are acoustic receivers.

37. The method of claim 35, wherein the transducers disposed in the environment are acoustic receivers and the transducers mounted on the body are acoustic emitters.

38. The method of claim 35, wherein the transducers disposed in the environment are optical emitters and the transducers mounted on the body are optical receivers.

39. The method of claim 35, wherein the transducers disposed in the environment are optical receivers and the transducers mounted on the body are optical emitters.

40. The method of claim 35, wherein the transducers disposed in the environment are radio frequency emitters and the transducers mounted on the body are radio frequency receivers.

41. The method of claim 35, wherein the transducers disposed in the environment are radio frequency receivers and the transducers mounted on the body are radio frequency emitters.

42. The method of claim 35, wherein at the transducers mounted on the body are disposed so that, in substantially all orientations of the rigid body, at least one of the transducers mounted on the body is positioned to be able to complete a range measurement with at least three of the transducers disposed in the environment.

43. The method of claim 42, further comprising:

selecting one of the transducers mounted on the body and obtaining a range measurement between it and one of the transducers disposed in the environment.

44. A method for tracking a motion of a body comprising:

obtaining two types of measurements associated with the motion of the body, a first type comprising range measurement, and a second type comprising inertial measurement;

updating estimates of an orientation and a position of the body based on the second type of measurement; and

updating the estimate of the position of the body based on the first type of measurement, without first calculating a position estimate based only on the first type of measurement.

45. The method of claim 44, in which the first type of measurement comprises acoustic ranging.

46. The method of claim 44, further comprising updating the estimate of an orientation of the body based on the first type of measurement.

47. A method for tracking a motion of a body comprising:

obtaining two types of measurements associated with the motion of the body, a first type comprising range measurement, and a second type comprising angular inertial measurement;

updating an estimate of an orientation of the body based on the second type of measurement; and

updating the orientation estimate and an estimate of the position of the body based on the first type of measurement.