State estimator for rejecting noise and tracking and updating bias in inertial sensors and associated methods

• US 9,127,947 B2
• Filed: 05/18/2009
• Issued: 09/08/2015
• Est. Priority Date: 05/18/2009
• Status: Active Grant

• Current Assignee: University of Utah Research Foundation (State of Utah)
• Original Assignee: University of Utah Research Foundation (State of Utah)
• Inventors: Minor, Mark A., Johnson, Eric A., Morris Bamberg, Stacy J.
• Primary Examiner(s): Kundu, Sujoy
• Assistant Examiner(s): Ngon, Ricky
• Application Number:
  US12/467,881
• Publication Number:
  US 20100292943A1
• Time in Patent Office: 2,304 Days
• Field of Search: 702/33, 702/41, 702/57, 702 64- 70, 702/79, 702/82, 702 86- 89, 702/96, 702104-106, 702/110, 702/111, 702/113, 702/116, 702/141, 702/142, 702/179, 702180-182, 702189-191, 702193-195, 73/13.7, 73/13.8, 734/90, 735/10, 735/040.2, 73/17.7, 324612-614, 701/207, 701/220, 701/221, 235/105
• US Class Current: 1/1
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01R 31/2829 Testing of circuits in sensor or actuator systems testing of apparatus for measuring electric or magnetic variables G01R35/00; testing of indicating or recording apparatus G01D; in airbag systems B60R21/0173; checking gas analysers G01N33/007; monitoring or fail-safe circuits for electromagnets H01F7/1844

Abstract

A method and system for tracking and updating bias in an inertial sensor by determining a maximum bias drift and a noise band for a sensor, determining a prior bias value of the sensor, and measuring a current bias value of the sensor. The method and system can further include calculating a bias difference between the prior bias value and the current bias value, and updating the prior bias value with the current bias value if the current bias value is within the noise band and the bias difference is less than or equal to the maximum bias drift.

Claims

1. A method for tracking and updating bias in a sensor during an extended period of periodic motion in order to improve operational accuracy of the sensor, comprising:

determining a maximum bias drift for a sensor, the maximum bias drift comprising a maximum amount of drift in bias that is permitted to occur during a specified amount of time, such that when the maximum bias drift is exceeded, the maximum bias drift determination prevents bias values from being updated in the sensor;

determining a noise band for the sensor;

determining a prior bias value of the sensor;

measuring a current bias value of the sensor;

calculating by a processor a bias difference between the prior bias value and the current bias value; and

updating the prior bias value with the current bias value upon determining that the current bias value is within the noise band and that the bias difference is less than or equal to the determined maximum bias drift, the updating the prior bias value with the current bias value thereby eliminating accumulated error to improve the operational accuracy of the sensor.

2. The method of claim 1, wherein determining the prior bias value includes determining the prior bias value of the sensor and storing the prior bias value in a memory location associated with the sensor.

3. The method of claim 1, wherein updating the prior bias value further includes:

retrieving the prior bias value from the memory location;

calculating the bias difference between the prior bias value and the current bias value with an electronic processor functionally coupled to the memory location;

updating the prior bias value with the current bias value if the current bias value is within the noise band and the bias difference is less than or equal to the maximum bias drift; and

storing the updated prior bias value in the memory location.

4. The method of claim 1, wherein the sensor is a member selected from the group consisting of accelerometers, gyroscopes, and combinations thereof.

5. The method of claim 1, wherein the noise band is measured as peak-to-peak amplitude.

6. The method of claim 1, wherein updating the bias value occurs in real time.

7. The method of claim 1, wherein updating the bias value occurs in real time during gait motions of a subject.

8. The method of claim 1, wherein data from the sensor is filtered prior to updating the prior bias value.

9. The method of claim 1, wherein data from the sensor is low-pass filtered prior to updating the prior bias value.

10. The method of claim 9, wherein the data from the sensor is low-pass filtered with a cutoff frequency that is below a dominant noise frequency.

11. The method of claim 1, wherein determining a maximum bias drift and a noise band for the sensor is performed at room temperature.

12. A system for tracking and updating bias in a sensor during an extended period of periodic motion in order to improve operational accuracy of the sensor, comprising:

a sensor;

an electronic processor functionally coupled to the sensor; and

a memory device functionally coupled to the electronic processor and capable of receiving and storing data from the electronic processor, wherein the memory device has computer executable instructions stored thereon that when executed by the electronic processor, cause the electronic processor to perform the following;

determine a maximum bias drift for the sensor, the maximum bias drift comprising a maximum amount of drift in bias that is permitted occur during a specified amount of time, such that when the maximum bias drift is exceeded, the maximum bias drift determination prevents bias values from being updated in the sensor,

determine a noise band for the sensor,

determine a prior bias value of the sensor,

measure a current bias value of the sensor,

calculate a bias difference between the prior bias value and the current bias value, and

update the prior bias value with the current bias value upon determining that the current bias value is within the noise band and that the bias difference is less than or equal to the determined maximum bias drift, thereby eliminating accumulated error to improve the operational accuracy of the sensor.

13. The system of claim 12, further comprising a shoe, wherein the shoe contains the sensor, the electronic processor, and the memory device.

14. The system of claim 12, further comprising an electronic view screen functionally coupled to the electronic processor and capable of displaying data derived from the sensor.

15. The system of claim 12, further comprising an electronic input device capable of interaction with the electronic processor.

16. A method for tracking and updating bias of a sensor during an extended period of periodic motion in order to improve operational accuracy of the sensor, comprising:

determining a maximum bias drift for a sensor, the maximum bias drift comprising a maximum amount of drift in bias that is permitted occur during a specified amount of time, such that when the maximum bias drift is exceeded, the maximum bias drift determination prevents bias values from being updated in the sensor;

determining a noise band for the sensor;

retrieving a prior bias value from a memory location functionally associated to the sensor;

obtaining a current bias value from the sensor;

calculating a bias difference between the prior bias value and the current bias value with an electronic processor functionally coupled to the memory location;

replacing the prior bias value with the current bias value upon determining that the current bias value is within the noise band and that the bias difference is less than or equal to the determined maximum bias drift, the replacing the prior bias value with the current bias value thereby eliminating accumulated error to improve the operational accuracy of the sensor; and

storing the updated prior bias value in the memory location.

17. The method of claim 16, wherein data from the sensor is electronically filtered prior to updating the prior bias value.

18. The method of claim 16, wherein data from the sensor is low-pass filtered prior to updating the prior bias value.

19. The method of claim 18, wherein the data from the sensor is low-pass filtered with a cutoff frequency that is below a dominant noise frequency.

20. The method of claim 16, wherein updating the bias value occurs in real time.

21. The method of claim 16, wherein updating the bias value occurs in real time during gait motions of a subject.