Heading confidence interval estimation

• US 10,132,829 B2
• Filed: 08/23/2013
• Issued: 11/20/2018
• Est. Priority Date: 03/13/2013
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: Zheng, Yuan, Lin, Shang-Hung, Keal, Kerry
• Primary Examiner(s): Charioui, Mohamed
• Assistant Examiner(s): Delozier, Jeremy
• Application Number:
  US13/975,016
• Publication Number:
  US 20140278183A1
• Time in Patent Office: 1,915 Days
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01P 15/00 Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

An inertial measurement system is disclosed. The inertial measurement system has an accelerometer processing unit that generates a calibrated accelerometer data. The inertial measurement system further includes a magnetometer processing unit generates a calibrated magnetometer data, and a gyroscope processing unit generates a calibrated gyroscope data. Using the calibrated accelerometer data, the calibrated magnetometer data, and the calibrated gyroscope data, the inertial measurement system generates a heading angle error indicative of the accuracy of the heading angle error.

Claims

1. An inertial measurement system comprising:

an accelerometer processing unit including an accelerometer sensor configured to sense acceleration of a device in motion to generate raw accelerometer data, the accelerometer processing unit configured to calibrate the raw acceleration data to generate an accelerometer output;

a magnetometer processing unit including a magnetometer sensor configured to sense magnetic field of the device in motion to generate raw magnetometer data, the magnetometer processing unit including a magnetometer calibration unit configured to calibrate the raw magnetometer data to generate a magnetometer output,

wherein the raw magnetometer data and/or the raw accelerometer data include a heading error;

a summer configured to combine the accelerometer output and the magnetometer output to generate a summer output;

a gyroscope processing unit including a gyroscope sensor, a gyroscope calibration unit, and a gyroscope integration unit, the gyroscope sensor configured to sense an angular velocity of the device in motion to generate raw angular velocity data, the gyroscope calibration unit configured to calibrate the raw angular velocity data to generate a calibrated angular velocity data, and the gyroscope integration unit configured to integrate the calibrated angular velocity data to generate a gyroscope output;

a sensor fusion configured to combine the gyroscope output and the summer output and to perform a quaternion operation on the combined gyroscope output and summer output to generate a quaternion output representative of an orientation of the device in motion, the orientation of the device in motion including heading angle and/or confidence value used to calculate a confidence interval indicative of bounds of a heading angle uncertainty, the heading angle uncertainty representing a confidence in value of a heading angle estimation in view of the heading error in the raw magnetometer data and/or raw accelerometer data, wherein a smaller confidence in value indicates a higher reliability in the heading angle estimation and a larger confidence in value indicates a lower reliability in the heading angle estimation.

2. The inertial measurement system of claim 1, wherein the confidence interval is related to a statistical property of an inner product of an accelerometer vector and a magnetometer vector, the accelerometer vector being a vector related to the accelerometer output and the magnetometer vector being a vector related to the magnetometer output.

3. The inertial measurement system of claim 1, wherein the accelerometer processing unit further includes a first comparator operable to compare the accelerometer output to a predefined reference, represented in world coordinates, to generate a first comparison output.

4. The inertial measurement system of claim 3, wherein the magnetometer calibration unit is configured to generate the magnetometer output in world coordinates.

5. The inertial measurement system of claim 4, wherein the magnetometer processing unit further includes a second comparator configured to compare the magnetometer output to the predefined reference, in world coordinates, and to generate a second comparison output.

6. The inertial measurement system of claim 1, further including a converter responsive to the summer output.

7. The inertial measurement system of claim 1, further including a transform block responsive to the quaternion output to generate the orientation of the device in motion.

8. The inertial measurement system of claim 1, wherein the accelerometer sensor, the magnetometer sensor, and a gyroscope sensor reside on one semiconductor chip and the accelerometer calibration unit, the magnetometer calibration unit, a gyroscope calibration unit, the gyroscope integration unit, and the sensor fusion, reside on another semiconductor chip.

9. The inertial measurement system of claim 1, wherein the accelerometer processing unit, the magnetometer processing unit, a gyroscope processing unit, and the sensor fusion reside on the same semiconductor chip.

10. The inertial measurement system of claim 1, wherein the inertial measurement system uses the raw accelerometer data as a reference to a gravity direction and uses the raw magnetometer data as a reference to a magnetic north direction.

11. The inertial measurement system of claim 3, wherein the accelerometer calibration unit, the magnetometer calibration unit, a gyroscope calibration unit and the first comparator are implemented in hardware or software.

12. The inertial measurement system of claim 3, wherein the magnetometer calibration unit and the first comparator are implemented in hardware or software.

13. The inertial measurement system of claim 1, wherein a gyroscope calibration unit and the gyroscope integration unit are implemented in hardware or software.

14. The inertial measurement system of claim 1, further including an inverse quaternion block responsive to the quaternion output and configured to perform inverse quaternion and to generate an inverse quaternion output, wherein the accelerometer calibration unit is responsive to the inverse quaternion output.

15. An inertial measurement system comprising:

an accelerometer processing unit including an accelerometer sensor configured to sense of a device in motion to generate raw acceleration data, the accelerometer sensor adding bias and noise to the raw acceleration data, the raw acceleration data with bias and noise defining an accelerometer output, the accelerometer processing unit further including a calibration and gravity extraction block responsive to the acceleration output and configured to calibrate the acceleration output to generate calibrated accelerometer data;

a magnetometer processing unit including a magnetometer sensor configured to sense magnetic field, the magnetometer sensor adding bias and noise to the sensed magnetic field defining a magnetometer output, the magnetometer processing unit further including a magnetometer calibration unit responsive to the magnetometer output and configured to calibrate the magnetometer output to generate a calibrated magnetometer data;

a summer configured to combine the accelerometer output and the magnetometer output to generate a summer output;

a sensor fusion responsive to the junction output and configured to generate quaternion output;

a gyroscope processing unit including a gyroscope sensor, a gyroscope calibration unit, and a gyroscope integration unit, the gyroscope sensor adding bias and noise to the angular velocity, the gyroscope sensor configured to sense an angular velocity of the device in motion to generate raw angular velocity data, the angular velocity with the bias and noise defining a gyroscope output, the gyroscope calibration unit configured to calibrate the raw angular velocity data to generate a calibrated angular velocity data, and the gyroscope integration unit configured to integrate the calibrated angular velocity data to generate a gyroscope output;

sensor fusion configured to combine the gyroscope output and the summer output and perform a quaternion operation to generate a quaternion output representative of an orientation of the device in motion, the orientation of the device in motion including heading angle and/or confidence value used to calculate a confidence interval indicative of bounds of a heading angle uncertainty, the heading angle uncertainty representing a confidence in value of a heading angle estimation of heading error in the raw magnetometer data and/or raw accelerometer data, wherein a smaller confidence in value indicates a higher reliability in the heading angle estimation and a larger confidence in value indicates a lower reliability in the heading angle estimation;

an inverse quaternion block responsive to the quaternion output and configured to perform inverse quaternion and to generate an inverse quaternion output,

wherein the accelerometer calibration unit is responsive to the inverse quaternion output, further wherein the inertial measurement system is operable to generate the heading angle and/or confidence value.

16. The inertial measurement system of claim 15, wherein the operation of the junction is summing.

17. A method of estimating heading using an inertial measurement system comprising:

receiving raw accelerometer data including bias and noise from an accelerometer sensor sensing acceleration of a device in motion;

calibrating the received raw accelerometer data to generate a calibrated accelerometer data to generate accelerometer output;

receiving raw magnetometer data from a magnetometer sensor sensing magnetic field of the device in motion, the magnetometer sensor adding bias and noise to the magnetic field of the device in motion;

a magnetometer calibration unit calibrating the magnetometer output to generate a magnetometer output;

performing an operation on the accelerometer output and the magnetometer output to generate an operation output;

a sensor fusion generating a quaternion output based on the operation output;

calibrating a gyroscope data to generate a calibrated gyroscope data;

integrating the quaternion output and the calibrated gyroscope data;

performing inverse quaternion on the quaternion output to generate an inverse quaternion output; and

generating a confidence interval indicative of bounds of a heading angle uncertainty, the heading angle uncertainty representing a confidence in value of a heading angle estimation in view of error in the raw magnetometer data and/or raw accelerometer data.

18. The method of estimating heading, as recited in claim 17, further including comparing the calibrated accelerometer data to a predefined reference in world coordinates to generate a first comparison output.

19. The method of estimating heading, as recited in claim 18, further including comparing the calibrated magnetometer data to the predefined reference in world coordinates to generate a second comparison output.

20. The method of estimating heading, as recited in claim 19, further including generating an estimate of the bounds of a heading angle uncertainty by combining the first and the second comparison outputs.

21. The inertial measurement system of claim 17, wherein the operation is summing.