Method of correcting the orientation of a freely installed accelerometer in a vehicle

• US 9,581,615 B2
• Filed: 10/01/2012
• Issued: 02/28/2017
• Est. Priority Date: 09/30/2011
• Status: Active Grant

• Current Assignee: Appy Risk Technologies Limited (Trak Global Group Ltd.)
• Original Assignee: Ntelligent Mechatronic Systems Incorporated
• Inventors: Basir, Otman A., Jamali, Seyed Hamidreza, Miners, William Ben, Toonstra, Jason
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US13/632,554
• Publication Number:
  US 20130081442A1
• Time in Patent Office: 1,611 Days
• Field of Search: 734/93, 735/10, 73/13.8, 734/88, 340438-439, 340/425.5, 701/31.4, 701/70
• US Class Current: 1/1
• CPC Class Codes: G01C 21/185 for gravity
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G01S 19/53 Determining attitude

Abstract

A vehicle monitoring system includes an accelerometer installed in the vehicle in an unknown orientation. The system infers the orientation of the accelerometer in the vehicle from the acceleration signals. The proposed method detects and corrects the orientation in two steps. In the first step, the gravity vector is used to estimate the orientation in the vertical plane. Then, based on the acceleration data collected during the vehicle movement, the heading of the vehicle is estimated and the orientation within the horizontal plane is corrected.

Claims

1. A method for orienting an accelerometer in a vehicle including the steps of:

a) determining a gravity vector relative to an accelerometer orientation by averaging accelerometer information from each of three axes of the accelerometer over time while the vehicle is moving;

b) reorienting the accelerometer information based upon the gravity vector determined in said step a); and

c) filtering the reoriented accelerometer information from said step b); and

d) determining a forward direction of the vehicle to determine a horizontal orientation of the accelerometer relative to the vehicle, including applying principal component analysis to the filtered reoriented accelerometer information recorded by the accelerometer during a trip.

2. The method of claim 1 wherein said step d) is based upon a determination that change in direction of acceleration in a plane orthogonal to the gravity vector is below a threshold.

3. The method of claim 1 wherein said step d) is based upon a determination that the vehicle is traveling forward based upon speed information from the vehicle.

4. The method of claim 1 further including:

using a previous determination of horizontal orientation from a previous trip as an initial accelerometer orientation relative to the vehicle.

5. The method of claim 1 further including the step of calculating a moving average with a variable time window size of a gravity component on each of the three axes.

6. The method of claim 2 wherein said step d) is performed without reference to information other than acceleration information from the accelerometer.

7. The method of claim 1 wherein said step d) further includes the step of expurgating the accelerometer information after said step a).

8. The method of claim 7 wherein said step of expurgating includes the step of monitoring an angle between the forward and lateral components of the accelerometer information during the trip.

9. The method of claim 8 further including the step of determining that a resultant of forward and lateral components of the accelerometer information coincides with the forward direction of the vehicle.

10. The method of claim 1 wherein said step d) is performed after determining that a change in a heading of the vehicle does not exceed a threshold.

11. The method of claim 1 wherein said step c) includes the step of applying a median filter to the reoriented accelerometer information from said step b).