Systems and methods for calibrating unstable sensors

• US 10,514,258 B2
• Filed: 08/31/2017
• Issued: 12/24/2019
• Est. Priority Date: 09/09/2016
• Status: Active Grant

• Current Assignee: NextNav, LLC
• Original Assignee: NextNav, LLC
• Inventors: Dormody, Michael, Pattabiraman, Ganesh, Kumar, Abijith, Wolf, Thomas, Parsons, Gary, Gates, Christian, Joseph, Deepak, Nagarajan, Badrinath
• Primary Examiner(s): Jimenez, Anthony R
• Application Number:
  US15/692,142
• Publication Number:
  US 20170363423A1
• Time in Patent Office: 845 Days
• Field of Search: 701408
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 21/10 by using measurements of speed or acceleration G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• 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: G01C 5/06 by using barometric means
• CPC Class Codes: G01L 27/002 Calibrating, i.e. establishing true relation between transducer output value and value to be measured, zeroing, linearising or span error determination
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 5/012 Identifying whether indoors or outdoors
• CPC Class Codes: G01S 5/017 Detecting state or type of motion
• CPC Class Codes: G01S 5/02 using radio waves using satellite radio beacon systems for determining position G01S19/00

Abstract

Calibrating an unstable sensor of a mobile device. Systems and methods for calibrating a sensor of a mobile device determine a first estimated position of the mobile device without using any measurement from the sensor of the mobile device, generate a second estimated position of the mobile device using a measurement from the sensor, estimate a sensor error of the sensor using the first estimated position and the second estimated position, and use the sensor error to determine a calibration value for adjusting one or more measurements from the sensor.

Claims

1. A method for calibrating a sensor of a mobile device, the method comprising:

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor,

wherein the sensor is a pressure sensor of the mobile device, and

wherein the calibration value is determined by;

identifying a pressure sensor calibration equation that includes calibration coefficient values;

identifying temperature measurements of the pressure sensor and corresponding sensor error measurements for the pressure sensor, wherein each temperature measurement of the identified temperature measurements was measured when the pressure sensor made a corresponding measurement of pressure that was used to determine a corresponding sensor error measurement of the identified sensor error measurements;

determining calibration coefficient adjustment values by performing a polynomial fit using the identified temperature measurements and corresponding sensor error measurements;

determining an adjusted pressure sensor calibration equation by using the calibration coefficient adjustment values to adjust the calibration coefficient values of the pressure sensor calibration equation; and

determining the calibration value using the adjusted pressure sensor calibration equation.

2. The method of claim 1, wherein the first estimated position includes a first altitude and the second estimated position includes a second altitude, and wherein the sensor error is estimated by:

determining a difference in altitude between the first estimated position and the second estimated position;

determining an estimated difference in pressure between the first estimated position and the second estimated position by applying a scaling factor to the difference in altitude, wherein the scaling factor specifies a change in pressure per an amount of vertical distance; and

setting the sensor error to the estimated difference in pressure.

3. The method of claim 1, wherein the method comprises:

adjusting a measurement from the sensor by the calibration value.

4. A method for calibrating a sensor of a mobile device, the method comprising:

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor,

wherein the sensor error is estimated by;

determining a difference in distance between the first estimated position and the second estimated position;

determining an estimated difference in pressure between the first estimated position and the second estimated position by applying a scaling factor to the difference in distance; and

setting the sensor error to the estimated difference in pressure.

5. The method of claim 4, wherein the first estimated position includes a first altitude and the second estimated position includes a second altitude, and the difference in distance is a difference in altitude.

6. The method of claim 4, wherein the method comprises:

adjusting a measurement from the sensor by the calibration value, wherein the calibration value is set to the sensor error or an average of the sensor error and other previously stored sensor errors.

7. One or more non-transitory machine-readable media embodying program instructions that, when executed by one or more machines, cause the one or more machines to implement a method for calibrating a sensor of a mobile device, the method comprising:

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor,

wherein the sensor is a pressure sensor of the mobile device, and

wherein the calibration value is determined by;

identifying a pressure sensor calibration equation that includes calibration coefficient values;

identifying temperature measurements of the pressure sensor and corresponding sensor error measurements for the pressure sensor, wherein each temperature measurement of the identified temperature measurements was measured when the pressure sensor made a corresponding measurement of pressure that was used to determine a corresponding sensor error measurement of the identified sensor error measurements;

determining calibration coefficient adjustment values by performing a polynomial fit using the identified temperature measurements and corresponding sensor error measurements;

determining an adjusted pressure sensor calibration equation by using the calibration coefficient adjustment values to adjust the calibration coefficient values of the pressure sensor calibration equation; and

determining the calibration value using the adjusted pressure sensor calibration equation.

8. The one or more non-transitory machine-readable media of claim 7, wherein the first estimated position includes a first altitude and the second estimated position includes a second altitude, and wherein the sensor error is estimated by:

determining a difference in altitude between the first estimated position and the second estimated position;

determining an estimated difference in pressure between the first estimated position and the second estimated position by applying a scaling factor to the difference in altitude, wherein the scaling factor specifies a change in pressure per an amount of vertical distance; and

setting the sensor error to the estimated difference in pressure.

9. The one or more non-transitory machine-readable media of claim 7, wherein the method comprises:

adjusting a measurement from the sensor by the calibration value.

10. One or more non-transitory machine-readable media embodying program instructions that, when executed by one or more machines, cause the one or more machines to implement a method for calibrating a sensor of a mobile device, the method comprising:

determining a first estimated position of the mobile device without using any measurement from the sensor of the mobile device;

generating a second estimated position of the mobile device using a measurement from the sensor;

estimating a sensor error of the sensor using the first estimated position and the second estimated position; and

using the sensor error to determine a calibration value for adjusting one or more measurements from the sensor,

wherein the sensor error is estimated by;

determining a difference in distance between the first estimated position and the second estimated position;

determining an estimated difference in pressure between the first estimated position and the second estimated position by applying a scaling factor to the difference in distance; and

setting the sensor error to the estimated difference in pressure.

11. The one or more non-transitory machine-readable media of claim 10, wherein the first estimated position includes a first altitude and the second estimated position includes a second altitude, and the difference in distance is a difference in altitude.

12. The one or more non-transitory machine-readable media of claim 10, wherein the method comprises:

adjusting a measurement from the sensor by the calibration value,

wherein the calibration value is set to the sensor error or an average of the sensor error and other previously stored sensor errors.