Motion tracking system

• US 20040143176A1
• Filed: 12/23/2003
• Published: 07/22/2004
• Est. Priority Date: 04/17/1998
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Foxlin, Eric M.
• Granted Patent: US 7,395,181 B2
• Time in Patent Office: Days
• US Class Current: 600/395
• 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 two types of measurements associated with the motion of the body, one of the types comprising acoustic measurement;

updating an estimate of either an orientation or a position of the body based on one of the two types of measurement; and

updating the estimate based on the other of the two types of measurements.

2. The method of claim 1 in which one of the types of measurement comprises acoustic ranging.

3. The method of claim 1 in which the other of the types of measurement comprises inertial measurement.

4. The method of claim 1 in which the estimate is of orientation.

5. 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; and

a processor coupled to the two sensor systems and configured to update an estimate of wither 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.

6. 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.

7. The tracking device of claim 6 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.

8. The tracking device of claim 6 wherein the set of one or more acoustic sensors includes two or more acoustic sensors.

9. The tracking device of claim 6 wherein

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

and

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

10. 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 an 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.

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 an 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.