Method and apparatus for differential scale factor calibration in differential odometry systems integrated with GPS

• US 6,230,100 B1
• Filed: 01/31/1997
• Issued: 05/08/2001
• Est. Priority Date: 01/31/1997
• Status: Expired due to Term

• Current Assignee: Continental Automotive Systems, Inc. (Continental AG)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Geier, George Jeffrey
• Primary Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US08/792,124
• Time in Patent Office: 1,558 Days
• Field of Search: 701/213, 701/214, 701/215, 701/216, 701/217, 701/206, 701/207, 701/224, 701/200, 701/220, 701/221, 340/988, 340/995, 340/990, 342/357, 342/457, 342/357.14, 342/357.12, 73/178 R, 73/1.77, 235/95 R
• US Class Current: 701/216
• CPC Class Codes: G01C 22/025 Differential odometers

Abstract

Calibration of a differential scale factor associated with left and right wheels of a vehicle having a terrestrial navigation system. The terrestrial navigation system includes a GPS receiver integrated with a dead reckoning system. The dead reckoning system has wheel sensors coupled to the left and right wheels. The calibration of the differential scale factor includes: determining a heading change with the dead reckoning system, using the determined heading change to determine an open loop heading, determining an error in the differential scale factor based on the open loop heading and an alternate heading, and using the error in the differential scale factor to adjust an initial value of the differential scale factor.

Claims

1. A method for calibrating a differential scale factor associated with left and right wheels of a movable vehicle in which a terrestrial navigation system is installed, said terrestrial navigation system comprised of a GPS receiver integrated with a dead reckoning system, said dead reckoning system utilizing wheel sensors coupled to said left and right wheels, said method comprising the steps of:

determining a heading change based upon said dead reckoning system, said differential scale factor of said dead reckoning system having an initial value wherein said differential scale factor is indicative of a difference in size of tires attached to the left and right wheels;

using said determined heading change derived from said dead reckoning system to determine an open loop heading;

summing successive determined values of said open loop headings over a time period based upon said movable vehicles traveling a predetermined distance;

determining an error in said differential scale factor based upon said summed successive open loop headings and a heading computed by said GPS receiver; and

using said error in said differential scale factor to adjust said initial value of said differential scale factor.

2. The method of claim 1 wherein said steps of determining a heading change, using said determined heading change and determining an error in said differential scale factor are repeated to further adjust said differential scale factor.

3. The method of claim 1 wherein said predetermined distance is one kilometer.

4. The method of claim 1 wherein said error in said differential scale factor is tested for reasonableness before being used to adjust said differential scale factor.

5. The method of claim 1 wherein said open loop heading is initialized to a value based upon a GPS heading from said GPS receiver.

6. The method of claim 1 wherein said initial value of said differential scale factor is one.

7. The method of claim 1 wherein said alternate heading is determined at a time when said movable vehicle has traveled a predetermined distance.

8. The method of claim 1 wherein said error in said differential scale factor is adjusted in real time.

9. The method of claim 1 wherein said dead reckoning system includes wheel sensors installed on front wheels of said movable vehicle.

10. The method of claim 1 wherein said dead reckoning system includes wheel sensors installed on rear wheels of said movable vehicle.

11. The method of claim 1 wherein said dead reckoning system includes wheel sensors installed on both front and rear wheels of said movable vehicle.

12. A method for calibrating a differential scale factor associated with left and right wheels of a movable vehicle in which a terrestrial navigation system is installed, said terrestrial navigation system comprised of a GPS receiver integrated with a dead reckoning system, said dead reckoning system utilizing wheel sensors coupled to said left and right wheels, said method comprising the steps of:

determining a heading change based upon said dead reckoning system, said differential scale factor of said dead reckoning system having an initial value wherein said differential scale factor is indicative of a difference in size of tires attached to the left and right wheels;

using said determined heading change derived from said dead reckoning system to determine an open loop heading;

determining an error in said differential scale factor based upon said summed successive open loop headings and a heading computed by said GPS receiver, wherein said error in said differential scale factor is tested for reasonableness before being used to adjust said differential scale factor by comparing the square of said error in said differential scale factor with a residual variance; and

using said error in said differential scale factor to adjust said initial value of said differential scale factor.

13. An apparatus for calibrating a differential scale factor associated with left and right wheels of a movable vehicle, said apparatus comprising:

wheels sensors, coupled to said left and right wheels of said movable vehicle, for determining distance traveled by said left and right wheels;

means for determining a heading change of said movable vehicle based upon said distance traveled by said left and right wheels, said differential scale factor having an initial value wherein said differential scale factor is indicative of a difference in size of tires attached to the left and right wheels;

means, responsive to said means for determining said heading change, for determining an open loop heading;

means, responsive to said means for determining said open loop heading, for summing successive determined values of said open loop headings over a time period based upon said movable vehicle traveling a predetermined distance;

a GPS receiver for computing a heading of said movable vehicle;

means for determining an error in said differential scale factor based upon said summed successive open loop headings and said heading of said GPS receiver; and

means, responsive to said error in said differential scale factor, for adjusting said initial value of said differential scale factor.

14. The apparatus of claim 13 further including means for repeatedly adjusting said differential scale factor based upon additional determined errors in said differential scale factor.

15. The apparatus of claim 13 wherein said predetermined distance is one kilometer.

16. The apparatus of claim 13 further including means for testing said error in said differential scale factor for reasonableness before being used to adjust said differential scale factor.

17. The apparatus of claim 16 wherein said means for testing includes means for comparing the square of said error in said differential scale factor with a residual variance.

18. The apparatus of claim 13 wherein said open loop heading is initialized to a value based upon a GPS heading from said GPS receiver.

19. The apparatus of claim 13 wherein said initial value of said differential scale factor is one.

20. The apparatus of claim 13 wherein said heading of said alternate means is determined at a time when said movable vehicle has traveled a predetermined distance.

21. The apparatus of claim 13 wherein said error in said differential scale factor is adjusted in real time.

22. The apparatus of claim 13 wherein said wheel sensors are installed on front wheels of said movable vehicle.

23. The apparatus of claim 13 wherein said wheel sensors are installed on rear wheels of said movable vehicle.

24. The apparatus of claim 13 wherein said wheel sensors are installed on both front and rear wheels of said movable vehicle.