System and Method for Calibrating Inertial Measurement Units

• US 20140150521A1
• Filed: 12/03/2013
• Published: 06/05/2014
• Est. Priority Date: 12/03/2012
• Status: Active Grant

• Current Assignee: Vibrado Holdings, Inc.
• Original Assignee: Vibrado Technologies, Inc.
• Inventors: Jacobson, Quinn A., Kuo, Cynthia
• Granted Patent: US 9,599,634 B2
• Time in Patent Office: Days
• US Class Current: 73/1.38
• 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: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

Inertial measurement units attached to a non-rigid body may measure a common motion event when the body changes direction of travel. Acceleration measurements made by the inertial measurement units of the event are used to determine a common reference direction which in turn can be used to derive, individually for each inertial measurement unit, a new orientation intended to be a better representation of the actual orientation of the inertial measurement unit.

Claims

1. A method for calibrating sensor modules, the method comprising:

obtaining, from each of a plurality of sensor modules attached to a body, a direction measurement of an acceleration event occurring where the sensor module is located on the body, each direction measurement being derived from a present orientation of the sensor module and data on the acceleration event in the sensor module;

determining a common reference direction, the common reference direction determined from at least one of the direction measurements; and

determining, for at least one of the sensor modules, a new present orientation in which the sensor module would have provided a direction measurement, of the acceleration event occurring where the sensor module is located, that is equivalent to the common reference direction.

2. The method of claim 1, further comprising sending information to the at least one of the sensor modules, wherein the information enables the sensor module to use the new present orientation.

3. The method of claim 1, further comprising establishing, as a prerequisite to determining the common reference direction, that the acceleration events will be useful for calibration.

4. The method claim 3, wherein establishing that the acceleration events will be useful for calibration includes determining that acceleration magnitudes of the acceleration events are within a range.

5. The method of claim 3, wherein establishing that the acceleration events will be useful for calibration includes determining that acceleration magnitudes of the acceleration events are above a threshold size.

6. The method of claim 5, wherein threshold size is a threshold size for an acceleration magnitude component perpendicular to background force of gravity.

7. The method of claim 3, wherein establishing that the acceleration events will be useful for calibration includes determining that acceleration directions of the acceleration events from an axis parallel to background force of gravity are within a threshold range.

8. The method of claim 3, wherein establishing that the acceleration events will be useful for calibration includes determining that rates or change in rates of rotation measured by the sensor modules are below a threshold value.

9. The method of claim 1, further comprising establishing, as a prerequisite to determining the common reference direction, that the acceleration events are similar.

10. The method of claim 9, wherein establishing that the acceleration events are similar includes establishing that the acceleration events are similar in terms of any one or a combination of acceleration magnitude, duration of the acceleration events, amount of rotation measured by the sensor modules during the acceleration events, and direction of rotation measured by the sensor modules during the acceleration events.

11. The method of claim 1, wherein determining the common reference direction includes averaging the direction measurements of two or more acceleration events.

12. The method of claim 1, wherein determining the common reference direction includes assigning the direction measurement of one of the acceleration events to be the common reference direction.

13. The method of claim 1, wherein the common reference direction is obtained from the direction measurements of at least two of the sensor modules.

14. The method of claim 13, wherein new present orientations are determined for the at least two of the sensor modules.

15. The method of claim 1, wherein each new present orientation differs from the present orientation by an amount of yaw rotation about an axis parallel to background force of gravity, and the amount of yaw rotation is derived from the data from the accelerometer in the sensor module.

16. The method of claim 1, wherein each new present orientation differs from the present orientation by an amount of pitch rotation about an axis perpendicular to background force of gravity, and the amount of pitch rotation is derived from data from a magnetometer in the sensor module.

17. The method of claim 1, wherein each new present orientation differs from the present orientation by an amount of roll rotation about an axis perpendicular to background force of gravity, and the amount of roll rotation is derived from data from the magnetometer in the sensor module.

18. The method of claim 1, wherein the acceleration events include linear acceleration events, the direction measurements include direction measurements of linear acceleration, and the common reference direction is determined from at least one of the direction measurements of linear acceleration.

19. The method of claim 1, wherein the acceleration events include angular acceleration events, the direction measurements include measurements of the pivots of rotation, and the common reference direction is determined from at least one of the measurements of the pivots of rotation.

20. A system for calibrating sensor modules, the system comprising

a plurality of sensor modules;

and

a processor communicatively coupled to each of the sensor modules,

wherein the processor is configured to obtain, from each of the plurality of sensor modules, a direction measurement of an acceleration event occurring where the sensor module is located, each direction measurement having been derived from a present orientation of the sensor module and data on the acceleration event in the sensor module, and

wherein the processor is configured to determine a common reference direction from at least one of the direction measurements, and

wherein the processor is configured to determine, for at least one of the sensor modules, a new present orientation in which the sensor module would have provided a direction measurement, of the acceleration event occurring where the sensor module is located, that is equivalent to the common reference direction.

21-38. -38. (canceled)

39. A non-transitory computer readable medium having a stored computer program embodying instructions, which when executed by a computer, causes the computer to perform one or more steps for calibrating sensor modules, the computer readable medium comprising:

instructions for obtaining, from each of a plurality of sensor modules, a direction measurement of an acceleration event occurring where the sensor module is located, each direction measurement having been derived from a present orientation of the sensor module and data on the acceleration event in the sensor module;

instructions for determining a common reference direction from at least one of the direction measurements to determine; and

instructions for determining, for at least one of the sensor modules, a new present orientation in which the sensor module would have provided a direction measurement, of the acceleration event occurring where the sensor module is located, that is equivalent to the common reference direction.

40-41. -41. (canceled)