Calibrating sensor unit orientation for use in a vehicle monitoring system

Patent metadata

Field	Value
Publication number	US-10712362-B2
Application number	US-201815906977-A
Country	US
Kind code	B2
Filing date	Feb 27, 2018
Priority date	May 1, 2017
Publication date	Jul 14, 2020
Grant date	Jul 14, 2020

Abstract

This disclosure relates to a system and method for calibrating sensors upon installation in a vehicle. The system includes a sensor set configured to generate output signals conveying vectors of acceleration of the vehicle. The system determines a three-dimensional orientation of the sensor set in relation to the vehicle. The system converts output signals from the sensor set into vectors of acceleration of the vehicle.

First claim

What is claimed is:

1. A system configured to calibrate orientation of an accelerometer in a vehicle that includes a sensor set, wherein the sensor set is configured to generate output signals conveying vectors of acceleration of the vehicle, wherein the sensor set has a three-dimensional orientation in relation to the vehicle, the system configured to couple with the vehicle, the system comprising:
one or more processors configured to:
determine a gravity vector, wherein the determination of the gravity vector is based on the output signals generated by the sensor set, and wherein the determination of the gravity vector is further based on a determination that the vehicle is stopped;
perform a comparison of a rate of acceleration of the vehicle with a threshold level of acceleration to determine whether a magnitude of the rate of acceleration of the vehicle has exceeded the threshold level of acceleration such that the magnitude of the rate of acceleration of the vehicle is sufficient to assume the vehicle is not turning left or right but moving straight;
determine the vehicle is longitudinally accelerating and not turning left or right, wherein the determination is based on the comparison of the rate of acceleration of the vehicle with the threshold level of acceleration, wherein the magnitude of the rate of acceleration of the vehicle has exceeded the threshold level of acceleration;
subsequent to the determination that the vehicle is longitudinally accelerating, determine a longitudinal vector of the vehicle based on the generated output signals; and
determine the three-dimensional orientation of the sensor set in relation to the vehicle, wherein determination of the three-dimensional orientation is based on the gravity vector and the longitudinal vector.

2. The system of claim 1 , wherein the one or more processors are further configured to:
convert output signals generated by the sensor set into one or more vectors of acceleration of the vehicle, wherein conversion is based on the three-dimensional orientation of the sensor set in relation to the vehicle.

3. The system of claim 2 , wherein conversion of the output signals includes multiplication of the output signals of the sensor set with an inverted rotation matrix.

4. The system of claim 1 , wherein the determination that the vehicle is stopped is based on a signal generated by a speed sensor of the vehicle, wherein the speed sensor is included in the sensor set of the vehicle.

5. The system of claim 1 , wherein the rate of acceleration of the vehicle is determined based on a signal generated by a speed sensor of the vehicle, wherein the speed sensor is included in the sensor set of the vehicle.

6. The system of claim 1 , wherein the determination that the magnitude of the rate of acceleration of the vehicle has exceeded the threshold level of acceleration is further based on a determination that the magnitude of the rate of acceleration has exceeded the threshold level for at least a specified duration.

7. The system of claim 1 , wherein the threshold level corresponds to at least 0.1 g.

8. The system of claim 1 , wherein determining the longitudinal vector includes a subtraction of the gravity vector from a current acceleration vector during a duration when the vehicle has been determined to be longitudinally accelerating.

9. The system of claim 1 , wherein the one or more processors are further configured to:
determine a lateral vector that is orthogonal to both the gravity vector and the longitudinal vector;
construct a rotation matrix based on the gravity vector, the longitudinal vector, and the lateral vector; and
invert the rotation matrix,
wherein determining the three-dimensional orientation of the sensor set in relation to the vehicle is based on the inverted rotation matrix.

10. The system of claim 9 , wherein determination of the lateral vector includes normalization of the longitudinal vector and performance of a cross product of the gravity vector and the longitudinal vector.

11. The system of claim 1 , wherein determination of the gravity vector is performed more than twice and results of the determination are aggregated.

12. The system of claim 1 , wherein determination of the longitudinal vector is performed repeatedly for a duration spanning at least 10 minutes and results of the determination are aggregated.

13. The system of claim 1 , wherein the vectors of acceleration of the vehicle include three orthogonal vectors of acceleration.

14. The system of claim 1 , wherein the sensor set includes the accelerometer.

15. The system of claim 1 , wherein the sensor set includes the accelerometer and a magnetometer.

16. The system of claim 1 , wherein the sensor set includes a three-axis accelerometer, a three-axis magnetometer, and a three-axis gyroscope.

17. A method to calibrate orientation of an accelerometer in a vehicle that includes a sensor set, wherein the sensor set generates output signals conveying vectors of acceleration of the vehicle, wherein the sensor set has a three-dimensional orientation in relation to the vehicle, the method comprising:
determining a gravity vector, wherein the determination of the gravity vector is based on the output signals generated by the sensor set, and wherein the determination of the gravity vector is further based on a determination that the vehicle is stopped;
performing a comparison of a rate of acceleration of the vehicle with a threshold level of acceleration to determine whether a magnitude of the rate of acceleration of the vehicle has exceeded the threshold level of acceleration such that the magnitude of the rate of acceleration of the vehicle is sufficient to assume the vehicle is not turning left or right but moving straight;
determining the vehicle is longitudinally accelerating and not turning left or right, wherein the determination is based on the comparison of the rate of acceleration of the vehicle with the threshold level of acceleration, wherein the magnitude of the rate of acceleration of the vehicle has exceeded the threshold level of acceleration;
subsequent to the determination that the vehicle is longitudinally accelerating, determining a longitudinal vector of the vehicle based on the generated output signals; and
determining the three-dimensional orientation of the sensor set in relation to the vehicle, wherein determining the three-dimensional orientation is based on the gravity vector and the longitudinal vector.

18. The method of claim 17 , further comprising:
converting output signals generated by the sensor set into one or more vectors of acceleration of the vehicle, wherein conversion is based on the three-dimensional orientation of the sensor set in relation to the vehicle.

19. The method of claim 18 , further comprising:
determining a lateral vector that is orthogonal to the gravity vector and the longitudinal vector;
constructing a rotation matrix based on the gravity vector, the longitudinal vector, and the lateral vector; and
inverting the rotation matrix,
wherein determining the three-dimensional orientation of the sensor set in relation to the vehicle is based on the inverted rotation matrix, and
wherein converting the output signals includes multiplying the output signals of the sensor set with the inverted rotation matrix.

20. The method of claim 17 , wherein the determination that the vehicle is stopped is based on a signal generated by a speed sensor of the vehicle, wherein the speed sensor is included in the sensor set of the vehicle,

Assignees

• Smartdrive Systems Inc

Inventors

• Sljivar Slaven
• Forney David
• Freitas Mark
• Deninger Daniel A
• Griswold Jeffrey
• Palmer Jason

Classifications

• G01C25/005

  initial alignment, calibration or starting-up of inertial devices · CPC title

• G01C25/00

  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 title

• G01P15/18

  in two or more dimensions · CPC title

• G01P21/02

  of speedometers · CPC title

• G01P21/00 Primary

  Testing or calibrating of apparatus or devices covered by the preceding groups · CPC title