Motion-tracking

• US 20020194914A1
• Filed: 08/21/2002
• Published: 12/26/2002
• Est. Priority Date: 04/21/2000
• Status: Active Grant

• Current Assignee: Thales Visionix Incorporated (Thales SA)
• Original Assignee: Intersense Incorporated
• Inventors: Altshuler, Yury, Foxlin, Eric
• Granted Patent: US 6,681,629 B2
• Time in Patent Office: Days
• US Class Current: 73/514.01
• CPC Class Codes: A61B 2503/22 Motor vehicles operators, e.g. drivers, pilots, captains
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/1114 Tracking parts of the body
• CPC Class Codes: G01C 21/12 executed aboard the object being navigated; Dead reckoning

Abstract

Inertial trackers have been successfully applied to a wide range of head mounted display (HMD) applications including virtual environment training, VR gaming and even fixed-base vehicle simulation, in which they have gained widespread acceptance due to their superior resolution and low latency. Until now, inertial trackers have not been used in applications which require tracking motion relative to a moving platform, such as motion-base simulators, virtual environment trainers deployed on board ships, and live vehicular applications including helmet-mounted cueing systems and enhanced vision or situational awareness displays, to the invention enables the use of inertial head-tracking systems on-board moving platforms by computing the motion of a “tracking” Inertial Measurement Unit (IMU) mounted on the HMD relative to a “reference” IMU rigidly attached to the moving platform.

Claims

1. A system for tracking the motion of an object relative to a moving reference frame, comprising:

a first inertial sensor mounted on the tracked object;

a second inertial sensor mounted on the moving reference frame; and

an element coupled to said first and second inertial sensors and configured to determine an orientation of the object relative to the moving reference frame based on the signals from the first and second inertial sensor.

20. The system of claim 1, in which the moving reference frame is associated with a vehicle, and the second inertial sensor comprises a pre-existing inertial measurement unit on a vehicle that was installed for the purpose of navigation.

21. The system of claim 1, in which the first and second inertial sensors each comprises at least six linear accelerometers and associated processors to extract three angular inertial signals and three linear accelerations.

2. The system of claim I in which the first and second inertial sensors each comprises three angular inertial sensors selected from the set of angular accelerometers, angular rate sensors, and angular position gyroscopes.

3. The system of claim 2, in which the angular inertial sensors comprise angular rate sensors, and the orientation of the object relative to the moving reference frame is determined by integrating a relative angular rate signal determined from the angular rate signals measured by the first and second inertial sensors.

4. The system of claim 3, further comprising a non-inertial measuring subsystem for making independent measurements related to the orientation of the object relative to the moving reference frame, and using them for correcting any drift that may occur in the inertial orientation integration.

5. The system of claim 4, in which the non-inertial measuring subsystem is selected from the set of optical, acoustic, magnetic, RF, or electromagnetic technologies.

6. The system of claim 2, in which the determination of relative orientation includes computing the orientation of the object with respect to a fixed inertial reference frame using the signals from the first inertial sensor,

computing the orientation of the moving reference frame with respect to the same fixed inertial reference frame using the signals from the second inertial sensor, and

computing the relative orientation based on the two orientations.

7. The system of claim 6, further comprising a drift corrector for correcting inertial drift in the determined orientation of the object with respect to the inertial reference frame or of the moving reference frame with respect to the inertial reference frame.

8. The system of claim 7, in which said drift corrector includes sensors for determining tilt with respect to earth'"'"'s gravitational field.

9. The system of claim 7, where said drift corrector includes sensors for determining heading with respect to earth'"'"'s magnetic field.

10. The system of claim 6, further comprising a drift corrector for correcting inertial drift in the determined orientation of the object with respect to the moving reference frame by using non-inertial sensors to independently measure the relative orientation.

11. The system of claim 2, in which the first and second inertial sensors each further comprises three linear accelerometers.

12. The system of claim 11, further comprising an element for calculating the position of the object relative to the moving reference frame.

13. The system of claim 12, in which the calculating element double-integrates a relative linear acceleration signal computed from the linear accelerometer signals measured by the first and second inertial sensors.

14. The system of claim 13, in which calculation of said relative linear acceleration signal includes compensation for tangential, Coriolis and centripetal acceleration effects caused by the angular velocity and angular acceleration of the moving reference frame.

15. The system of claim 14, in which the compensation terms are calculated using the angular velocity or angular acceleration of the moving reference frame measured by the second inertial sensor.

16. The system of claim 13, in which no compensation for the effect of gravity on the accelerometers is made.

17. The system of claim 12, in which the calculation of the position of the object relative to the moving reference frame includes:

computing the position of the object with respect to a fixed inertial reference frame using the signals from the first inertial sensor,

computing the position of the moving reference frame with respect to the same fixed inertial reference frame using the signals from the second inertial sensor, and

computing the relative position based on the two individual positions.

18. The system of claim 17, further comprising a drift corrector for correcting inertial drift in the determined position of the object with respect to the inertial reference frame or of the moving reference frame with respect to the inertial reference frame.

19. The system of claim 18, in which the drift corrector includes sensors for measuring position of both the object and the moving reference frame with respect to landmarks fixed in common inertial reference frame.

22. A method comprising determining an orientation of an object relative to a moving reference frame based on signals from two inertial sensors mounted respectively on the object and on the moving reference frame.