Calibrating sensor measurements on mobile devices

• US 8,626,465 B2
• Filed: 09/20/2010
• Issued: 01/07/2014
• Est. Priority Date: 03/30/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Moore, Christopher, King, Brian Michael, Vieta, William Matthew, Tu, Xiaoyuan, Piemonte, Patrick
• Primary Examiner(s): KUNDU, SUJOY K
• Application Number:
  US12/886,494
• Publication Number:
  US 20110246117A1
• Time in Patent Office: 1,205 Days
• Field of Search: 702/92, 702/93, 702/99, 702/130, 702/136, 702150-153, 701/211, 701/216, 701/300, 340/995.12, 340/995.24, 340/995.27
• US Class Current: 702/99
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• 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: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature

Abstract

Sensor measurements are used to detect when a device incorporating the sensor is stationary. While the device is stationary, sensor measurements at a current device temperature are used to estimate model parameters. The model parameters can be used in a state estimator to provide an estimated attitude that can be provided to other applications. In some implementations, the estimated attitude can be used to mitigate interference in other sensor measurements.

Claims

1. A computer-implemented method performed by one or more processors of a mobile device, comprising:

receiving one or more sensor measurements from a sensor onboard the mobile device;

determining if the device is stationary based on the one or more sensor measurements;

at a first time, upon determining that the device is stationary, calculating one or more model parameters for a current temperature from the sensor measurements, wherein calculating the one or more model parameters includes calculating a measurement bias based on the one or more sensor measurements that are received when the mobile device is determined to be stationary at the first time;

storing, in a calibration database, a calibration point, the calibration point comprising the measurement bias and the current temperature; and

at a second time that occurs after the first time, estimating an attitude of the device using the measurement bias based on a temperature measured at the second time and the temperature of the calibration point.

2. The method of claim 1, further comprising:

mitigating interference in other sensor measurements using the estimated attitude.

3. The method of claim 1, where the sensor measurements are angular rate and the model parameters include measurement bias and temperature slope.

4. The method of claim 1, where determining whether the device is stationary, comprises:

calculating a variance from window averaged sensor measurements; and

determining if the variance exceeds a threshold.

5. The method of claim 1, where calculating one or more model parameters, comprises:

calculating a linear fit of calibration points and temperature slope.

6. The method of claim 1, where estimating an attitude comprises:

estimating temperature using a first estimation filter having a filter state including temperature and temperature rate; and

estimating an attitude of the device using a second estimation filter having a filter state including local attitude error and measurement bias.

7. The method of claim 6, where the first and second estimation filters are Kalman filter formulations.

8. The method of claim 1, further comprising:

maintaining a running average of temperature compensated angular rates as an estimate of measurement bias.

9. The method of claim 8, where maintaining a running average comprises:

filtering angular rates using a low pass filter with a dynamic update rate that is selected based on magnitudes of the angular rates.

10. A system for estimating an attitude of a mobile device, comprising:

a sensor onboard the mobile device;

a processor coupled to the sensor and configured to execute instructions which cause the processor to perform operations comprising;

receiving one or more sensor measurements from the sensor;

determining if the device is stationary based on the one or more sensor measurements;

at a first time, upon determining that the device is stationary, calculating one or more model parameters for a current temperature from the sensor measurements, wherein calculating the one or more model parameters includes calculating a measurement bias based on the one or more sensor measurements that are received when the mobile device is determined to be stationary at the first time

storing, in a calibration database, a calibration point, the calibration point comprising the measurement bias and the current temperature; and

at a second time that occurs after the first time, estimating an attitude of the device using the measurement bias based on a temperature measured at the second time and the temperature of the calibration point.

11. The system of claim 10, where the processor is configured to execute instructions to mitigate interference in other sensor measurements using the estimated attitude.

12. The system of claim 10, where the sensor measurements are angular rate and the model parameters include measurement bias and temperature slope.

13. The system of claim 10, where the processor is configured to execute instructions to calculate a variance from window averaged sensor measurements, and to determine if the variance exceeds a threshold.

14. The system of claim 10, where the processor is configured to execute instructions to calculate a linear fit of calibration points and temperature slope.

15. The system of claim 10, where the processor is configured to execute instructions to estimate temperature using a first estimation filter having a filter state including temperature and temperature rate, and to estimate an attitude of the device using a second estimation filter having a filter state including local attitude error and measurement bias.

16. The system of claim 15, where the first and second estimation filters are Kalman filter formulations.

17. The system of claim 10, where the processor is configured to execute instructions to maintain a running average of temperature compensated angular rates as an estimate of measurement bias.

18. The system of claim 17, where the processor is configured to execute instructions to filter angular rates using a low pass filter with a dynamic update rate that is selected based on magnitudes of the angular rates.

19. The system of claim 10, where the sensor is a gyroscope.

20. A non-transitory storage device storing a computer program operable to cause one or more processors of a mobile device to perform operations comprising:

receiving one or more sensor measurements from a sensor onboard the mobile device;

determining if the device is stationary based on the one or more sensor measurements;

at a first time, upon determining that the device is stationary, calculating one or more model parameters for a current temperature from the sensor measurements, wherein calculating the one or more model parameters includes calculating a measurement bias based on the one or more sensor measurements that are received when the mobile device is determined to be stationary at the first time;

storing, in a calibration database, a calibration point, the calibration point comprising the measurement bias and the current temperature; and

at a second time that occurs after the first time, estimating an attitude of the device using the measurement bias based on a temperature measured at the second time and the temperature of the calibration point.