Systems and methods for 3-axis accelerometer calibration with vertical sample buffers

• US 9,459,277 B2
• Filed: 02/19/2013
• Issued: 10/04/2016
• Est. Priority Date: 02/19/2013
• Status: Active Grant

• Current Assignee: CalAmp Corporation
• Original Assignee: CalAmp Corporation
• Inventors: Hergesheimer, Peter, Sprague, Todd, Dlagnekov, Alexandre
• Primary Examiner(s): Beaulieu, Yonel
• Assistant Examiner(s): KLEINMAN, LAIL A
• Application Number:
  US13/770,920
• Publication Number:
  US 20140236519A1
• Time in Patent Office: 1,323 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G01S 19/14 specially adapted for specific applications

Abstract

Systems and methods for the calibration of 3-axis accelerometers using vertical sample buffers in accordance embodiments of the invention are disclosed. In one embodiment, a telematics system includes a processor, an acceleration sensor, a velocity sensor, and a memory configured to store an acceleration alignment application, wherein the acceleration alignment application configures the processor to receive a velocity information sample using the velocity sensor, determine vehicular acceleration information along at least one vehicle axes using the velocity information sample, receive at least one acceleration sensor acceleration information sample using the acceleration sensor, determine a plurality of vertical vector samples using the vehicular acceleration information, calculate an average vertical vector sample using at least one of the vertical vector samples, and calibrate at least one of the vehicle axes to an acceleration sensor axis using the vehicular acceleration information, the acceleration sensor acceleration sample, and the average vertical vector sample.

Claims

1. A telematics system, comprising:

a processor;

an acceleration sensor connected to the processor determining acceleration information along a set of acceleration sensor axes comprising a first accelerometer axis;

a velocity sensor connected to the processor and determining velocity information along axes of a vehicle and heading information, where the axes of a vehicle comprise a vehicular forward axis, a vehicular lateral axis, and a vehicular vertical axis and a memory connected to the processor and storing an acceleration alignment application and a vertical sample buffer, where the vertical sample buffer stores a number of vertical vector samples;

wherein the acceleration alignment application directs the processor to;

receive a velocity information sample using the velocity sensor;

determine vehicular acceleration information along at least one vehicle axes using the velocity information sample;

receive at least one acceleration sensor acceleration information sample using the acceleration sensor;

determine a plurality of vertical vector samples using the vehicular acceleration information;

store at least one of the determined plurality of vertical vector samples using the vertical sample buffer;

calculate an average vertical vector sample using at least one of the stored vertical vector samples; and

calibrate the first acceleration axis to the vehicular forward axis using the vehicular acceleration information, the at least one acceleration sensor acceleration sample, and the average vertical vector sample by computing orthogonal vectors based on the cross product of every combination of the acceleration sensor acceleration information along the vehicular forward axis, the vehicular lateral axis, and the vehicular vertical axis, thereby calibrating the orientation of the accelerometer so that the first accelerometer axis corresponds to the vehicular forward axis.

2. The telematics system of claim 1, wherein the vertical sample buffer is a circular buffer stores a fixed number of vertical vector samples.

3. The telematics system of claim 2, wherein the acceleration alignment application further directs the processor to replace the oldest vertical vector sample stored in the vertical sample buffer once the fixed number of vertical vector samples have been stored using the vertical sample buffer.

4. The telematics system of claim 3, wherein the acceleration alignment application further directs the processor to associate a vector sample metadata with a vector sample, where the vector sample metadata includes a timestamp.

5. The telematics system of claim 3, wherein the acceleration alignment application further directs the processor to:

associate axis calibration metadata with the at least one calibrated axes; and

recalibrate the calibrated vehicles axes using the acceleration sensor acceleration information samples, the vehicular acceleration sample, the stored at least one vertical vector sample, the vector sample metadata, and the axis calibration metadata.

6. The telematics system of claim 1, wherein:

the velocity sensor is a Global Positioning System (GPS) receiver having a GPS sampling rate;

the velocity information determined using the GPS receiver is determined at the GPS sampling rate;

each piece of velocity information determined using the GPS receiver has an associated velocity information error, where the velocity information error is a measure of the difference between the determined velocity information and the true velocity information; and

the acceleration alignment application further directs the processor to calculate the average vertical vector sample to compensate for the velocity information errors.

7. The telematics system of claim 1, wherein the acceleration alignment application further directs the processor to calculate the average vertical vector sample once a number of vertical vector samples have been stored in the buffer.

8. The telematics system of claim 7, wherein the number of vertical vector samples is determined based on performance requirements of the telematics system.

9. The telematics system of claim 8, wherein:

the velocity sensor determines velocity information at a velocity sensor sample rate;

the performance requirements of the telematics system are based on a delay between the motion of the telematics system and the time the calibration of at least one of the vehicle axes to an acceleration sensor axis in the at least one acceleration sensor axes is completed; and

the number of vertical vector samples utilized to determine the average vertical vector is based on the velocity sensor sample rate and the delay.

10. The telematics system of claim 1, wherein the acceleration alignment application further directs the processor to:

determine an updated average vertical acceleration vector using the stored vertical vectors and the calibrated vehicle axes; and

recalibrate the calibrated vehicles axes using the using the acceleration sensor acceleration information samples, the vehicular acceleration sample, and the updated average vertical acceleration vector.

11. A method for aligning a vehicle'"'"'s axes using a telematics system mounted in a vehicle having at least one vehicle axes, comprising:

receiving at least one velocity information sample using a telematics system;

determining vehicular acceleration information along at least one vehicle axis using velocity information sample and the telematics system, where the at least one vehicle axes comprises a vehicular forward axis, a vehicular lateral axis, and a vehicular vertical axis;

receiving at least one acceleration sensor acceleration information sample using the telematics system;

determining a plurality of vertical vector samples using the vehicular acceleration information and the telematics system;

storing at least one of the determined plurality of vertical vector samples using the telematics system;

calculating an average vertical vector sample using at least one of the stored vertical vector samples and the telematics system; and

calibrating a first acceleration axis to the vehicular forward axis based on the vehicular acceleration information, the at least one acceleration sensor acceleration sample, the average vertical vector sample by computing orthogonal vectors based on the cross product of every combination of the acceleration sensor acceleration information along the vehicular forward axis, the vehicular lateral axis, and the vehicular vertical axis, thereby calibrating the orientation of the accelerometer so that the first accelerometer axis corresponds to the vehicular forward axis using the telematics system.

12. The method of claim 11, wherein the telematics system stores a fixed number of vertical vector samples.

13. The method of claim 12, further comprising replacing the oldest stored vertical vector sample once the fixed number of vertical vector samples has been stored using the telematics system.

14. The method of claim 13, further comprising associating vector sample metadata with a vertical vector sample using the telematics system, where the vector sample metadata comprises a timestamp.

15. The method of claim 13, further comprising:

associating axis calibration metadata with the at least one calibrated axes using the telematics system; and

recalibrating the calibrated vehicles axes based on the acceleration sensor acceleration information samples, the vehicular acceleration sample, the stored at least one vertical vector sample, the vector sample metadata, and the axis calibration metadata using the telematics system.

16. The method of claim 11, wherein:

the telematics unit includes a Global Positioning System (GPS) receiver having a GPS sampling rate;

the velocity information determined using the telematics system is determined at the GPS sampling rate;

each piece of velocity information determined using the telematics system has an associated velocity information error, where the velocity information error is a measure of the difference between the determined velocity information and the true velocity information; and

calculating the average vertical vector sample using the telematics system compensating for the velocity information errors.

17. The method of claim 11, further comprising calculating the average vertical vector sample using the telematics system once a number of vertical vector samples have been stored.

18. The method of claim 17, wherein the number of vertical vector samples is determined based on performance requirements of the telematics system.

19. The method of claim 18, further comprising calculating the number of vertical vector samples utilized in determining the average vertical vector based on a velocity sensor sample rate using the telematics system.

20. The method of claim 11, further comprising:

determining an updated average vertical acceleration vector based on the stored vertical vectors and the calibrated vehicle axes using the telematics system; and

recalibrating the calibrated vehicles axes based on the acceleration sensor information samples, the vehicular acceleration sample, and the updated average vertical acceleration vector using the telematics system.