Forward-looking altitude detector

• US 20090312975A1
• Filed: 06/11/2008
• Published: 12/17/2009
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Wyck Loomis, Peter Van
• Granted Patent: US 7,856,336 B2
• Time in Patent Office: Days
• US Class Current: 702/96
• CPC Class Codes: G01C 21/12 executed aboard the object being navigated; Dead reckoning
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01C 5/00 Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels G01C3/20, G01C3/30 take precedence

Abstract

An altitude dead reckoning system using a speedometer and a forward-looking accelerometer for measuring changes in altitude.

Claims

1. A dead reckoning altimeter, comprising:

a speedometer to determine a forward speed;

an accelerometer to measure a forward acceleration; and

a DR altitude calculator to calculate an altitude change based on said speed and said measured acceleration.

2. The altimeter of claim 1, further comprising:

a yaw rate sensor to measure a yaw angle rate;

a yaw compensator to compensate said measured acceleration according to said yaw angle rate to determine a compensated acceleration; and

wherein

the DR altitude calculator is configured to use said compensated acceleration with said speed to calculate said altitude change.

3. The altimeter of claim 2, wherein:

the yaw compensator includes a yaw position compensator to compensate said measured acceleration for said yaw angle rate with a linear position offset respective to a turn radius line to determine said compensated acceleration.

4. The altimeter of claim 3, further comprising:

a return-to-position compensation detector to estimate said linear position offset using a double return loop having a first return to position after one of a clockwise loop or counterclockwise loop and a second return to position after the other of said clockwise loop or counterclockwise loop.

5. The altimeter of claim 2, wherein:

the yaw compensator includes a yaw alignment compensator configured to compensate said measured acceleration for said yaw angle rate with a yaw alignment angle to determine said compensated acceleration.

6. The altimeter of claim 5, further comprising:

a return-to-position compensation detector to estimate said yaw alignment angle using a double return loop having a first return to position after one of a clockwise loop or counterclockwise loop and a second return to position after the other of said clockwise loop or counterclockwise loop.

7. The altimeter of claim 1, further comprising:

a bias compensator to compensate said measured acceleration according to an accelerometer bias to determine a compensated acceleration, wherein

the DR altitude calculator is configured to use said compensated acceleration with said speed to calculate said altitude change.

8. The altimeter of claim 7, further comprising:

a Kalman filter configured to filter said altitude change with an external altitude fix to estimate said accelerometer bias.

9. The altimeter of claim 8, wherein:

said external altitude fix is derived from GNSS signals.

10. The altimeter of claim 8, wherein:

said external altitude fix is derived from map matching.

11. The altimeter of claim 7, further comprising:

a return-to-position compensation detector to estimate said accelerometer bias based on a return to position.

12. The altimeter of claim 7, further comprising:

a return-to-position compensation detector to estimate said accelerometer bias based on a return to position facing in an opposite direction.

13. The altimeter of claim 7, further comprising:

an incline angle calculator to calculate incline angle based on said compensated acceleration and rate of change of said speed; and

a restart bias detector to estimate said accelerometer bias at a restart of motion after a dormant time period based on a last said incline angle before said dormant time period.

14. The altimeter of claim 1, further comprising:

a GNSS receiver to determine a GNSS-based position including a GNSS-based altitude;

a yaw rate sensor to measure a yaw angle rate; and

wherein;

the DR altitude calculator is configured to use said yaw angle rate, said GNSS-based position, and said altitude change for providing a DR altitude having a better accuracy than said GNSS-based altitude.

15. The altimeter of claim 14, further comprising:

a map having floors of a parking garage;

wherein;

said DR altitude is used to distinguish between said floors when said floors are not reliably distinguished by said GNSS-based altitude.

16. A method for dead reckoning altitude, comprising:

determining a forward speed;

measuring a forward acceleration; and

calculating an altitude change based on said speed and said measured acceleration.

17. The method of claim 16, farther comprising:

measuring a yaw angle rate;

compensating said measured acceleration according to said yaw angle rate for determining a compensated acceleration; and

wherein;

calculating said altitude change includes using said compensated acceleration with said speed for calculating said altitude change.

18. The method of claim 17, wherein:

compensating said measured acceleration according to said yaw angle rate includes compensating for said yaw angle rate with a linear position offset respective to a turn radius line for determining said compensated acceleration.

19. The method of claim 18, further comprising:

estimating said linear position offset includes using a double loop having a first return to position after one of a clockwise loop or counterclockwise loop and a second return to position after the other of said clockwise loop or counterclockwise loop.

20. The method of claim 17, wherein:

compensating said measured acceleration according to said yaw angle rate includes compensating for said yaw angle rate with a yaw alignment angle for determining said compensated acceleration.

21. The method of claim 20, farther comprising:

estimating said yaw alignment angle includes using a double loop having a first return to position after one of a clockwise loop or counterclockwise loop and a second return to position after the other of said clockwise loop or counterclockwise loop.

22. The method of claim 16, further comprising:

compensating said measured acceleration according to an accelerometer bias to provide a compensated acceleration;

wherein

calculating said altitude change includes using said compensated acceleration with said speed for calculating said altitude change.

23. The method of claim 22, further comprising:

Kalman filtering said altitude change with an external altitude fix to estimate said accelerometer bias.

24. The method of claim 23, further comprising:

deriving said external altitude fix from GNSS signals.

25. The method of claim 23, wherein:

deriving said external altitude fix from map matching.

26. The method of claim 22, further comprising:

estimating said accelerometer bias based on a return to position.

27. The method of claim 22, further comprising:

estimating said accelerometer bias based on a return to position facing in an opposite direction.

28. The method of claim 22, further comprising:

calculating incline angle based on said compensated acceleration and rate of change of said speed; and

estimating said accelerometer bias at a restart of motion after a dormant time period based on a last said incline angle before said dormant time period and said measured acceleration.

29. The method of claim 16, further comprising:

determining a GNSS-based position including a GNSS-based altitude;

measuring a yaw angle rate; and

wherein;

calculating said altitude change includes using said yaw angle rate, said GNSS-based position, and said altitude change for providing a DR altitude having a better accuracy than said GNSS-based altitude.

30. The method of claim 29, further comprising:

providing an electronic map having floors of a parking garage; and

using said DR altitude for distinguishing between said floors when said floors are not reliably distinguished by said GNSS-based altitude.