SYSTEM AND METHOD FOR GYROSCOPE ERROR ESTIMATION

• US 20120259572A1
• Filed: 04/05/2012
• Published: 10/11/2012
• Est. Priority Date: 04/06/2011
• Status: Active Grant

• Current Assignee: UTI Limited Partnership
• Original Assignee: UTI Limited Partnership
• Inventors: Lachapelle, Gerard, Afzal, Muhammad Haris, Renaudin, Valerie
• Granted Patent: US 9,285,224 B2
• Time in Patent Office: Days
• US Class Current: 702/92
• 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) determining a rotational rate of change of said device around at least one axis;

b) determining an overall magnetic field vector of a magnetic field local to said device;

c) determining a rate of change of said magnetic field field vector;

d) determining if said magnetic field is unchanging;

e) in the event said magnetic field is unchanging, generating estimated gyroscope errors using said rate of change of said magnetic field vector and said rotational rate of change of said device;

f) compensating for said gyroscope errors using said estimated 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 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 a norm for said rate of change of magnetic field vector for a predetermined time window.

5. A method according to claim 4 wherein step d) further comprises determining 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 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 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 magnetic field is sensed using at least one magnetometer.

10. A method according to claim 1 wherein said rotational rate of change is sensed using at least one set of motion sensors.

11. A method according to claim 10 wherein said at least one set of motion sensors comprises at least one consumer grade rate gyroscope.

12. A method according to claim 9 wherein said at least one magnetometer comprises at least one anisotropic magneto-resistive magnetometer.

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

a) determining 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, determining a magnetic field vector for said magnetic field;

c) for each of said at least two periods of time, determining a rotational rate of change for said device;

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

14. A method according to claim 13 wherein said method is continuously repeated to continuously determine said errors in said readings from said gyroscope.

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

16. A method according claim 13 wherein said local magnetic field is sensed using a magnetometer.

17. A method according to claim 13 wherein said rotational rate of change is sensed using at least one set of motion sensors.

18. A method according 13 wherein said local magnetic field is unchanging when a rate of change of magnetic field strength measurements for said local magnetic field is close to zero.

19. 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) determining a rotational rate of change of said device around at least one axis;

b) determining an overall magnetic field vector of a magnetic field local to said device;

c) determining a rate of change of said magnetic field field vector;

d) determining if said magnetic field is unchanging;

e) in the event said magnetic field is unchanging, generating estimated gyroscope errors using said rate of change of said magnetic field vector and said rotational rate of change of said device;

f) compensating for said gyroscope errors using said estimated gyroscope errors.