Dynamic offset correction for calibration of MEMS sensor

• US 10,324,108 B2
• Filed: 02/05/2013
• Issued: 06/18/2019
• Est. Priority Date: 02/07/2012
• Status: Active Grant

• Current Assignee: Movella Incorporated (Movella Holdings, Inc.)
• Original Assignee: mCube, Inc.
• Inventors: Bhandari, Sanjay, Kelly, Joe
• Primary Examiner(s): Kundu, Sujoy K
• Assistant Examiner(s): Dinh, Lynda
• Application Number:
  US13/760,014
• Publication Number:
  US 20130218505A1
• Time in Patent Office: 2,324 Days
• Field of Search: 702104, 702116
• CPC Class Codes: G01C 21/08 involving use of the magnetic field of the earth
• CPC Class Codes: G01C 21/10 by using measurements of speed or acceleration G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass
• CPC Class Codes: G01P 15/14 by making use of gyroscopes gyroscopes per se G01C19/00
• 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

Abstract

A hand-held processor system for processing data from an integrated MEMS device disposed within a hand-held computer system and method. A dynamic offset correction (DOC) process computes 3-axis accelerometer biases without needing to know the orientation of the device. Arbitrary output biases can be corrected to ensure consistent performance A system of linear equations is formed using basic observations of gravity measurements by an acceleration measuring device, conditioned upon constraints in data quality, degree of sensed motion, duration, and time separation. This system of equations is modified and solved when appropriate geometric diversity conditions are met.

Claims

1. A system comprising:

a hand held computer device;

an integrated MEMS device disposed within the hand held computer device; and

a processor for processing data from the integrated MEMS device;

wherein the system is configured to;

determine, by the processor using the integrated MEMS device, that the hand held computer device has been stationary in a first position over a predetermined period of time; and

take a first measurement data, using the integrated MEMS device, with the hand held computer device in the first position;

determine, by the processor using the integrated MEMS device, that the hand held computer device has been stationary in a second position over the predetermined period of time; and

take a second measurement data, using the integrated MEMS device, with the hand held computer device in the second position;

determine, by the processor using the integrated MEMS device, that the hand held computer device has been stationary in a third position over the predetermined period of time; and

take a third measurement data, using the integrated MEMS device, with the hand held computer device in the third position;

determine, by the processor using the integrated MEMS device, that the hand held computer device has been stationary in a fourth position over the predetermined period of time; and

take a fourth measurement data, using the integrated MEMS device, with the hand held computer device in the fourth position;

wherein the first, second, third, and fourth measurement data taken at the first, second, third, and fourth positions, respectively, are uncorrelated with one another;

and

determine, using the processor, offset data for each of X-axis, Y-axis, and Z-axis using the first, second, third, and fourth measurement data; and

correct subsequent measurement data using the offset data for each of X-axis, Y-axis, and Z-axis to improve accuracy of measured sensor data;

wherein accuracy of measured sensor data is improved by taking the first, second, third, and fourth measurement data when the hand held computer device is stationary during normal operation without needing to know the orientation of the device, and the correcting of subsequent measurement data using the offset data is carried out dynamically during normal operation.

2. The system of claim 1, wherein the system is further configured to:

take measurement data, using the integrated MEMS device, without subjecting the hand held computer device in a stationary condition;

correct subsequent measurement data using the offset data for each of the X-axis, Y-axis, and Z-axis.

3. The system of claim 1 wherein the measurement data include at least four data points, and wherein the determining of offset data comprises building a 3×

3 matrix including the at least four data points.

4. The system of claim 1 wherein the determining of offset data is configured as a background process that constantly runs until geometric diversity conditions are met.

5. The system of claim 1 wherein the geometric diversity conditions are modified over time to improve accuracy after an initial period of convergence or completion using less stringent conditions.

6. The system of claim 1 further comprising a user-initiated calibration process including sensing, by the integrated MEMS device, user-initiated calibration data measurements as the user places the hand held computer device on a level surface and presses a button, or as the user performs a figure 8 maneuver in which the user moves the hand held computer device in a path having a shape resembling the number “

8,” and

determining user-initiated computed offset data using the user-initiated calibration data measurements.

7. The system of claim 1 wherein the integrated MEMS device comprises an integrated 3-axis MEMS accelerometer, or a 6-axis MEMS inertial sensing device including the MEMS accelerometer and a MEMS gyroscope, or 6-axis device including the MEMS accelerometer and a MEMS magnetometer.

8. The system of claim 1 wherein the determining of offset data comprises solving a matrix equation of the form:

Δ

{right arrow over (o)}=Y

where Δ

represents a matrix representing difference in measured acceleration at different time instances, o is a matrix of offsets along 3 axes, and Y represents a matrix of square of difference of accelerations at different time instances.

9. The method of claim 8, wherein the matrix equation comprises the following set of linear equations,

10. The system of claim 1 wherein the hand held computer device comprises a consumer device.

11. The system of claim 1 wherein correction module comprise a processor located on the same device as MEMS device or different device, on-chip logic, or software.

12. The system of claim 1 wherein measurement data comprise calibration data or measurement data.

13. An inertial sensor system for processing data from an integrated MEMS device, the inertial sensor system comprising:

a housing;

a non-transitory computer tangible memory for storing a plurality of non-transitory executable codes;

an integrated MEMS device disposed within the housing, the integrated MEMS device including a MEMS sensor;

a processor disposed within the housing and coupled to the tangible memory and the integrated MEMS device, wherein the processor is programmed to perform a plurality of functions by a plurality of non-transitory executable instructions;

wherein the inertial sensor system is configured to;

determine, by the processor using the integrated MEMS device, that integrated MEMS device has been stationary in a first position over a predetermined period of time; and

take a first measurement data, using the integrated MEMS device, with the integrated MEMS device in the first position;

determine, by the processor using the integrated MEMS device, that the integrated MEMS device has been stationary in a second position over the predetermined period of time; and

take a second measurement data, using the integrated MEMS device, with the integrated MEMS device in the second position;

determine, by the processor using the integrated MEMS device, that the integrated MEMS device has been stationary in a third position over the predetermined period of time; and

take a third measurement data, using the integrated MEMS device, with the integrated MEMS device in the third position;

determine, by the processor using the integrated MEMS device, that integrated MEMS device has been stationary in a fourth position over the predetermined period of time; and

take a fourth measurement data, using the integrated MEMS device, with the integrated MEMS device in the fourth position;

wherein the first, second, third, and fourth measurement data taken at the first, second, third, and fourth positions, respectively, are uncorrelated with one another;

and

determine, using the processor, offset data for each of X-axis, Y-axis, and Z-axis using the first, second, third, and fourth measurement data; and

correct subsequent measurement data using the offset data for each of X-axis, Y-axis, and Z-axis to improve accuracy of measured sensor data;

wherein accuracy of measured sensor data is improved by taking the first, second, third, and fourth measurement data when the hand held computer device is stationary during normal operation without needing to know the orientation of the device, and the correcting of subsequent measurement data using the offset data is carried out dynamically during normal operation.

14. The system of claim 13, wherein determining, by the processor, that the integrated MEMS device has been stationary comprises determining that measured sensor data has not changed over the predetermined period of time, in which gravity is a dominant acceleration component being sensed by the device.

15. The system of claim 14, wherein the predetermined period of time is 200 ms.

16. The system of claim 13 wherein the plurality of non-transitory executable instructions comprises:

executable code that programs the processor to initiate the determining of offset data in response to a user performing a predetermined maneuver with the inertial sensor system,

executable code that programs the processor to run the determining of offset data constantly as a background process until time period conditions, stationary conditions, geometric diversity conditions, or data limit conditions are met, or

executable code that programs the processor to initiate the determining of offset data in response to a user performing, with the inertial sensor system, a motion of the user retrieving the inertial sensor system from a first user position, holding inertial sensor system at a second user position, holding the inertial sensor system at a third user position, and then returning the inertial sensor system to the first user position.

17. The system of claim 13 wherein the plurality of non-transitory executable instructions comprises:

executable code that programs the processor to sense, by the MEMS sensor, user-initiated calibration data measurements as the user places the integrated MEMS device on a level surface and presses a button, or as the user performs a figure 8 maneuver in which the user moves the inertial sensor system in a path having a shape resembling the number “

8”

, and determining, by the processor, user-initiated computed offset data using the user-initiated calibration data measurements.

18. The system of claim 13 wherein the MEMS sensor comprises a MEMS accelerometer and the integrated MEMS device comprises:

an integrated 6-axis MEMS inertial sensing device including the MEMS accelerometer and a MEMS gyroscope,

an integrated 6-axis MEMS inertial sensing device including the MEMS accelerometer and a Magnetometer or an integrated 9-axis,

or a 10-axis inertial sensing device including the MEMS accelerometer and a MEMS gyroscope, a magnetometer, and a pressure sensor.

19. The system of claim 13 wherein the determining of offset data comprises solving a matrix equation:

Δ

{right arrow over (o)}=Y

where Δ

represents a matrix representing difference in measured acceleration at different time instances, o is a matrix of offsets along 3 axes, and Y represents a matrix of square of difference of accelerations at different time instances.

20. The method of claim 19, wherein the matrix equation comprises the following set of linear equations,

21. The system of claim 13 wherein the inertial sensor system is a hand-held system.

22. A method for processing data from an integrated MEMS device disposed within a computer device, the method comprising:

disposing, by a user, the computer device in a first position;

determining, by the computer device using the integrated MEMS device, that the computer device has been stationary in the first position over a predetermined period of time;

determining a first measurement data using the integrated MEMS device with the computer device in the first position;

disposing, by the user, the computer device in a second position;

determining, by the computer device using the integrated MEMS device, that the computer device has been stationary in the second position over the predetermined period of time;

taking a second measurement data using the integrated MEMS device with the computer device in the second position;

disposing, by the user, the computer device in a third position;

determining, by the computer device using the integrated MEMS device, that the computer device has been stationary in the third position over the predetermined period of time;

determining a third measurement data using the integrated MEMS device with the computer device in the third position;

disposing, by the user, the computer device in a fourth position;

determining, by the computer device using the integrated MEMS device, that the computer device has been stationary in the fourth position over the predetermined period of time;

determining a fourth measurement data using the integrated MEMS device with the computer device in the fourth position;

determining offsets for each of X-axis, Y-axis, and Z-axis using the first, second, third, and fourth measurement data;

wherein the first, second, third, and fourth measurement data taken at the first, second, third, and fourth positions, respectively, are uncorrelated with one another;

and

using the determined offsets for each of X-axis, Y-axis, and Z-axis to correct subsequent measurements with the integrated MEMS device to improve accuracy of measured sensor data;

wherein accuracy of measured sensor data is improved by taking the first, second, third, and fourth measurement data when the hand held computer device is stationary during normal operation without needing to know the orientation of the device, and the correcting of subsequent measurement data using the offset data is carried out dynamically during normal operation.

23. The method of claim 22 wherein the calibration data measurements include at least four data points, and wherein the determining of offset data comprises building a 3×

3 matrix including the at least four data points.

24. The method of claim 22 wherein determining offset data is initiated by a user performing a predetermined maneuver with the computer device;

wherein the predetermined maneuver comprises a motion of the user retrieving inertial sensor system from a first user position, holding the inertial sensor system at a second user position, holding the computer device at a third and then fourth user position.

25. The method of claim 22 wherein the determining of offset data is configured as a background process that constantly runs until geometric diversity conditions are met.

26. The method of claim 25 wherein the geometric diversity conditions are modified over time to improve accuracy after an initial period of convergence or completion using less stringent conditions.

27. The method of claim 22 further comprising a user-initiated calibration process including sensing, by the integrated MEMS device, user-initiated calibration data measurements as the user places the computer device on a level surface and presses a button, or as the user performs a figure 8 maneuver in which the user moves the computer device in a path having a shape resembling the number “

8”

, and determining, by the computer device, user-initiated computed offset data using the user-initiated calibration data measurements.

28. The method of claim 22 wherein the integrated MEMS device comprises an integrated 3-axis MEMS accelerometer, or a 6-axis MEMS inertial sensing device including the MEMS accelerometer and a MEMS gyroscope, or 6-axis device including the MEMS accelerometer and a MEMS magnetometer.

29. The method of claim 22 wherein determining of offset data comprises solving a matrix equation of the form:

Δ

{right arrow over (o)}=Y

where Δ

represents a matrix representing difference in measured acceleration at different time instances, o is a matrix of offsets along 3 axes, and Y represents a matrix of square of difference of accelerations at different time instances.

30. The method of claim 29, wherein the matrix equation comprises the following set of linear equations,