System and method for identifying a spatial relationship for use in calibrating accelerometer data

• US 8,494,710 B2
• Filed: 03/31/2011
• Issued: 07/23/2013
• Est. Priority Date: 03/31/2011
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Harvie, Richard
• Primary Examiner(s): Badii, Behrang
• Application Number:
  US13/077,067
• Publication Number:
  US 20120253585A1
• Time in Patent Office: 845 Days
• Field of Search: 701/33, 701/93, 701/472, 701/445, 701/500, 701/31.4, 701/74, 73/13.7, 734/95, 702/96, 705/4, 180/6.2, 180/6.24, 180/6.26, 340/665, 340/990, 340/995.28, 340/669, 244/3.2, 310/318
• US Class Current: 701/33.1
• CPC Class Codes: G07C 5/085 using electronic data carriers

Abstract

Methods and systems for identifying a spatial relationship between a frame of reference associated with an accelerometer mounted in a vehicle and a frame of reference associated with the vehicle Accelerometer data is received from an accelerometer and vehicle data is received from a vehicle network of the vehicle, a long term average of the accelerometer data is used to determine the direction of gravity in the frame of reference of the vehicle. In addition the vehicle date is used to determine changes in speed of the vehicle, and thus to determine the direction of the longitudinal axis of the vehicle in the frame of reference of the vehicle. From these determined directions, the spatial relationship between the frames of reference may be determined.

Claims

1. A system for identifying a spatial relationship between a first and a second frame of reference for use in calibrating accelerometer data, the first frame of reference being associated with an accelerometer mounted in a vehicle, and the second frame of reference being associated with the vehicle, the system comprising:

an interface for receiving accelerometer data from the accelerometer and vehicle data from a vehicle network of the vehicle, wherein the accelerometer data comprises vector data indicative of a direction of an acceleration of the accelerometer in the first frame of reference, and wherein the vehicle data comprises vehicle information indicative of an operative state of the vehicle; and

a data processing system, wherein the data processing system is arranged to;

derive, from a first set of said vector data received during a first period, a first vector indicative of a direction of a vertical axis of the vehicle within the first frame of reference;

identify, using the vehicle information, a second period in which the speed of the vehicle is changing;

derive, from a second set of said vector data received during the second period, a second vector indicative of a direction of a longitudinal axis of the vehicle within the first frame of reference; and

identify, based on the first and second vectors, a spatial relationship between the first and the second frame of reference.

2. The system of claim 1, wherein the system is arranged to identify, using the vehicle information, the first period.

3. The system of claim 2, wherein the system is arranged to identify, from the vehicle information, one or more of:

whether an ignition of the vehicle is on;

whether an engine of the vehicle is running; and

the speed of the vehicle, whereby to identify the first period.

4. The system of claim 1, wherein the system is configured to calculate a first average of the first set of vector data whereby to derive the first vector.

5. The system of claim 4 wherein the system is configured to use a filter to calculate the first average.

6. The system of claim 1, wherein the system is arranged to identify, from the vehicle information, a period in which the vehicle is braking whereby to identify the second period.

7. The system of claim 1, wherein the interface is arranged to receive vehicle information comprising information indicative of a speed of rotation of a shaft of the vehicle, and the data processing system is arranged to identify the second period using said information indicative of a speed of rotation of a driven shaft of the vehicle.

8. The system of claim 6, wherein the system is arranged to further determine magnitudes of acceleration from the vector data and to compare said magnitudes to a threshold whereby to identify the second period.

9. The system of claim 8 wherein the system is arranged to determine magnitudes of differences between the vector data and the first vector whereby to determine said magnitudes of acceleration.

10. The system of claim 8 wherein the system is arranged to determine magnitudes of components of the vector data orthogonal to the first vector whereby to determine said magnitudes of acceleration.

11. The system of claim 1, wherein the system is arranged to calculate a second average of the second set of vector data whereby to derive the second vector.

12. The system of claim 11 wherein the system is arranged to use a filter to calculate the second average.

13. The system of claim 11, wherein the system is arranged to derive a component of the second average which is orthogonal to the first vector whereby to determine the second vector.

14. The system of claim 1, wherein the system is arranged to identify a plurality of rotations based on the directions of the first and second vectors whereby to identify the spatial relationship between the first and the second frame of reference.

15. The system of claim 1, wherein the system is arranged to calibrate accelerometer data received by the interface using the identified spatial relationship.

16. The system of claim 1, comprising a memory arranged to store the first and second averages.

17. The system of claim 1, wherein the first and second frames of reference comprise three dimensional frames of reference.

18. The system of claim 1, wherein the vehicle network comprises an on-board vehicle network arranged to inter-connect a plurality of electronic control units of the vehicle.

19. The system of claim 1, wherein the interface comprises a connector arranged to connect to an on board diagnostics port of a vehicle.

20. A telematics unit for mounting in a vehicle, the telematics unit comprising:

an accelerometer arranged to provide accelerometer data comprising vector data indicative of a direction of an acceleration of the accelerometer in a first frame of reference;

an interface in communication with a vehicle network of the vehicle and arranged to receive vehicle data comprising vehicle information indicative of an operative state of the vehicle; and

a data processing system for identifying a spatial relationship between the first frame of reference and a second frame of reference associated with the vehicle for use in calibrating said accelerometer data, wherein the data processing system is arranged to;

derive, from a first set of said vector data received during a first period, a first vector indicative of a direction of a vertical axis of the vehicle within the first frame of reference;

identify, using the vehicle information, a second period in which the speed of the vehicle is changing;

derive, from a second set of said vector data received during the second period, a second vector indicative of a direction of a longitudinal axis of the vehicle within the first frame of reference; and

identify, based on the first and second vectors, a spatial relationship between the first and the second frame of reference.

21. A method for identifying a spatial relationship between a first and a second frame of reference for use in calibrating accelerometer data, the first frame of reference being associated with an accelerometer mounted in a vehicle, and the second frame of reference being associated with the vehicle, the method comprising:

receiving accelerometer data from the accelerometer and vehicle data from a vehicle network of the vehicle, wherein the accelerometer data comprises vector data indicative of a direction of an acceleration of the accelerometer in the first frame of reference, and wherein the vehicle data comprises vehicle information indicative of an operative state of the vehicle; and

deriving, from a first set of said vector data received during a first period, a first vector indicative of a direction of a vertical axis of the vehicle within the first frame of reference;

identifying, using the vehicle information, a second period in which the speed of the vehicle is changing;

deriving, from a second set of said vector data received during the second period, a second vector indicative of a direction of a longitudinal axis of the vehicle within the first frame of reference; and

identifying, based on the first and second vectors, a spatial relationship between the first and the second frame of reference.

22. The method of claim 21, comprising identifying, using the vehicle information, the first period.

23. The method of claim 22, comprising identifying one or more of:

whether an ignition of the vehicle is on;

whether an engine of the vehicle is running;

and the speed of the vehicle, whereby to identify the first period.

24. The method of claim 21, comprising calculating a first average of the first set of vector data whereby to derive the first vector.

25. The method of claim 24 comprising using a filter to calculate the first average.

26. The method of claim 21, comprising identifying, from the vehicle information, a period in which the vehicle is braking whereby to identify the second period.

27. The method of claim 21, comprising receiving vehicle information comprising information indicative of a speed of rotation of a shaft of the vehicle, and using said information indicative of a speed of rotation of a driven shaft of the vehicle whereby to identify the second period.

28. The method of claim 26, comprising determining magnitudes of acceleration from the vector data and comparing said magnitudes to a threshold whereby to identify the second period.

29. The method of claim 28 comprising determining magnitudes of differences between the vector data and the first vector whereby to determine said magnitudes of acceleration.

30. The method of claim 28 comprising determining magnitudes of components of the vector data orthogonal to the first vector whereby to determine said magnitudes of acceleration.

31. The method of claim 21, comprising calculating a second average of the second set of vector data whereby to derive the second vector.

32. The method of claim 31 comprising using a filter to calculate the second average.

33. The method of claim 31, comprising deriving a component of the second average which is orthogonal to the first vector whereby to determine the second vector.

34. The method of claim 21, comprising identifying a plurality of rotations based on the directions of the first and second vectors whereby to identify the spatial relationship between the first and the second frame of reference.

35. The method of claim 21, comprising calibrating accelerometer data received by the interface using the identified spatial relationship.

36. The method of claim 21, comprising storing the first and second averages.

37. The method of claim 21, wherein the first and second frames of reference comprise three dimensional frames of reference.

38. The method of claim 21, wherein the vehicle network comprises an on-board vehicle network arranged to inter-connect a plurality of electronic control units of the vehicle.

39. A computer readable storage medium storing computer readable instructions thereon for execution on a computing system to implement a method for identifying a spatial relationship between a first and a second frame of reference for use in calibrating accelerometer data, the first frame of reference being associated with an accelerometer mounted in a vehicle, and the second frame of reference being associated with the vehicle, the method comprising:

receiving accelerometer data from the accelerometer and vehicle data from a vehicle network of the vehicle, wherein the accelerometer data comprises vector data indicative of a direction of an acceleration of the accelerometer in the first frame of reference, and wherein the vehicle data comprises vehicle information indicative of an operative state of the vehicle; and

deriving, from a first set of said vector data received during a first period, a first vector indicative of a direction of a vertical axis of the vehicle within the first frame of reference;

identifying, using the vehicle information, a second period in which the speed of the vehicle is changing;

deriving, from a second set of said vector data received during the second period, a second vector indicative of a direction of a longitudinal axis of the vehicle within the first frame of reference; and

identifying, based on the first and second vectors, a spatial relationship between the first and the second frame of reference.