System and method for gyroscope error estimation

• US 9,285,224 B2
• Filed: 04/05/2012
• Issued: 03/15/2016
• Est. Priority Date: 04/06/2011
• Status: Active Grant

• Current Assignee: UTI Limited Partnership
• Original Assignee: UTI Limited Partnership
• Inventors: Afzal, Muhammad Haris, Renaudin, Valerie, Lachapelle, Gerard
• Primary Examiner(s): Satanovsky, Alexander
• Assistant Examiner(s): Kuan, John
• Application Number:
  US13/440,545
• Publication Number:
  US 20120259572A1
• Time in Patent Office: 1,440 Days
• US Class Current: 1/1
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01C 21/183 Compensation of inertial measurements, e.g. for temperature effects
• CPC Class Codes: G01C 21/20 Instruments for performing navigational calculations G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G06F 17/00 Digital computing or data processing equipment or methods, specially adapted for specific functions information retrieval, database structures or file system structures therefor G06F16/00

Abstract

Methods and systems for compensating for gyroscopic errors. A system uses magnetometers to detect and measure a magnetic field local to a personal navigation device. When the local magnetic field is quasi-static, the rate of change of the magnetic field is combined with the rotational rate of change of the device. This generates an estimated gyroscope error. The error can then be used to correct for time-varying inherent gyroscope errors.

Claims

1. A method for compensating for errors in a mobile gyroscope in a device, the method comprising:

a) measuring, by way of at least one set of motion sensors, a rotational rate of change of said device around at least one axis;

b) measuring, by way of at least one magnetometer, an overall magnetic field vector of a magnetic field local to said device;

c) calculating, by way of a processor, a rate of change of said magnetic field vector based on measurements from step b);

d) determining, by way of said processor, if said magnetic field is unchanging based on calculations from step c);

e) in the event said magnetic field is unchanging, estimating, by way of said processor, estimated gyroscope errors using said rate of change of said magnetic field vector calculated in step c) and said rotational rate of change of said device measured in step a); and

f) changing a navigational trajectory of said device based on said estimated gyroscope errors to thereby compensate for gyroscope errors.

2. A method according to claim 1 further comprising step g) continuously repeating steps a)-f) to account for time-varying gyroscope errors.

3. A method according to claim 1 wherein step d) comprises determining, by way of said processor, when a rate of change of magnetic field strength measurements is close to zero.

4. A method according to claim 3 wherein step d) further comprises determining, by way of said processor, a norm for said rate of change of said magnetic field vector for a predetermined time window.

5. A method according to claim 4 wherein step d) further comprises determining, by way of said processor, a rate of change for said norm to determine if said magnetic field local to said device is constant.

6. A method according to claim 1 wherein step e) comprises combining, by way of said processor, components of said rate of change of said magnetic field vector and said rotational rate of change of said device to generate said estimated gyroscope errors.

7. A method according to claim 6 wherein said step of combining is performed using an extended Kalman filter to generate said estimated gyroscope errors.

8. A method according to claim 1 wherein step e) comprises comparing, by way of said processor, said rate of change of said magnetic field vector with said rotational rate of change to result in said estimated gyroscopic errors.

9. A method according to claim 1 wherein said at least one set of motion sensors comprises at least one consumer grade rate gyroscope.

10. A method according to claim 1 wherein said at least one magnetometer comprises at least one anisotropic magneto-resistive magnetometer.

11. A method for determining errors in a gyroscope in a non-static device, the method comprising:

a) determining, by way of at least one magnetometer, at least two periods of time when a total local magnetic field is unchanging;

b) for each of said at least two periods of time, measuring, by way of said at least one magnetometer, a magnetic field vector for said magnetic field and a rate of change of said magnetic field vector;

c) for each of said at least two periods of time, measuring, by way of at least one set of motion sensors, a rotational rate of change for said device;

d) using an extended Kalman filter to estimate errors in readings from said gyroscope using the rate of change of said magnetic field vector determined in step b) and said rotational rate of change for said device; and

e) changing a navigational trajectory of said non-static device based on said errors estimated in step d).

12. A method according to claim 11 wherein said method is continuously repeated to continuously determine said errors in said readings from said gyroscope.

13. A method according to claim 11 wherein said method is executed on a personal navigation device.

14. A method according 11 wherein said total local magnetic field is unchanging when a rate of change of magnetic field strength measurements for said local magnetic field is close to zero.

15. A non-transitory computer readable media having encoded thereon computer readable instructions which, when executed, implements a method for compensating for errors in a handheld gyroscope in a device, the method comprising:

a) measuring, by way of at least one set of motion sensors, a rotational rate of change of said device around at least one axis;

b) measuring, by way of at least one magnetometer, an overall magnetic field vector of a magnetic field local to said device;

c) calculating, by way of a processor, a rate of change of said magnetic field vector based on measurements from step b);

d) determining, by way of a processor, if said magnetic field is unchanging based on calculations from step c);

e) in the event said magnetic field is unchanging, estimating, by way of a processor, estimated gyroscope errors using said rate of change of said magnetic field vector calculated in step c) and said rotational rate of change of said device measured in step a); and

f) changing a navigational trajectory of said device based on said estimated gyroscope errors to thereby compensate for gyroscope errors.