Method of calibrating a heading reference system

• US 9,157,747 B2
• Filed: 03/15/2013
• Issued: 10/13/2015
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Innovative Solutions and Support Incorporated
• Original Assignee: Innovative Solutions and Support Incorporated
• Inventors: Askarpour, Shahram
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): GOLDMAN, RICHARD A
• Application Number:
  US13/833,513
• Publication Number:
  US 20140278050A1
• Time in Patent Office: 942 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 21/20 Instruments for performing navigational calculations G01C21/24, G01C21/26 take precedence
• 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

Abstract

A method of calibrating a vehicle'"'"'s heading system, such as the attitude heading and reference system of an aircraft or the heading system of a ship, positioned along the Earth'"'"'s surface involves obtaining both actual and theoretical readings for the magnetometer of the heading system, and comparing these values to obtain calibration values for the heading system which are then averaged to obtain a universal average gain and offset for the magnetometer. The vehicle may be repositioned, such as to North, South, East, and west magnetic headings, with the procedure repeated at each of these headings, and the calibration values averaged, further increasing the accuracy.

Claims

1. A method for calibrating an aircraft attitude and reference heading system comprising at least one magnetometer, the method comprising the steps of:

selectively positioning an aircraft on the ground along the Earth'"'"'s surface;

obtaining an actual reading from the at least one magnetometer at a selected first magnetic heading for the positioned aircraft while the aircraft is stationary on the ground;

obtaining a set of theoretical magnetic field properties of the Earth at a location of the positioned aircraft, the obtained theoretical magnetic field properties comprising theoretical values for a horizontal intensity and a vertical intensity of the magnetic field at the location of the positioned aircraft;

computing a theoretical reading for the magnetometer at the first magnetic heading of the positioned aircraft based on at least the first magnetic heading, the associated attitude for the positioned aircraft, and the obtained theoretical values for the magnetic field at the location of the positioned aircraft;

comparing the obtained actual reading from the at least one magnetometer for the positioned aircraft at the first magnetic heading with the obtained theoretical magnetometer reading at the first magnetic heading for providing a first calibration value for the heading system at the first magnetic heading for the positioned aircraft;

selectively positioning the aircraft so as to select at least a second magnetic heading and repeating the obtaining, computing, and comparing steps for the at least second magnetic heading to provide at least a second calibration value for the heading system;

utilizing the first and the at least one second provided calibration values at the first and the at least one second magnetic headings of the aircraft to calculate a universal average gain and offset for the at least one magnetometer based on averaging the first and the at least one second calibration values; and

utilizing the universal average gain and offset to universally calibrate the heading system with respect to measurement errors.

2. The heading system calibration method in accordance with claim 1 wherein the aircraft is selectively positioned to at least four different magnetic headings.

3. The method in accordance with claim 2 wherein the four different selected magnetic headings for the aircraft comprise the North, South, East, and West magnetic headings for the aircraft during the calibration.

4. The method in accordance with claim 1 wherein the magnetometer comprises a triaxial magnetometer.

5. The method in accordance with claim 1 wherein the step of obtaining the set of theoretical magnetic field properties further comprises the step of obtaining the set from an organization that provides access to geophysical data.

6. The method in accordance with claim 1 wherein the aircraft has an associated engine and avionics, the calibration method being performed with the aircraft engine and avionics running.

7. The method in accordance with claim 1 wherein the magnetometer comprises a triaxial magnetometer and the equation for the aircraft magnetic heading is

8. The method in accordance with claim 1 further comprising:

utilizing at least one low pass filter to filter the calibration values of the plurality of magnetic headings for the positioned aircraft.

9. A method for calibrating a heading system for a vehicle comprising at least one magnetometer, the method comprising the steps of:

selectively positioning the vehicle along the Earth'"'"'s surface;

obtaining an actual reading from the at least one magnetometer at a selected first magnetic heading for the positioned vehicle while the vehicle is stationary on the Earth'"'"'s surface;

obtaining a set of theoretical magnetic field properties of the Earth at a location of the positioned vehicle, the obtained theoretical magnetic field properties comprising theoretical values for a horizontal intensity and a vertical intensity of the magnetic field at the location of the positioned vehicle;

computing a theoretical reading for the magnetometer at the first magnetic heading of the positioned vehicle based on at least the first magnetic heading, and the obtained theoretical values for the magnetic field at the location of the positioned vehicle;

comparing the obtained actual reading from the at least one magnetometer for the positioned vehicle at the first magnetic heading with the obtained theoretical magnetometer reading at the first magnetic heading for providing a first calibration value for the heading system at the first magnetic heading for the positioned vehicle;

selectively positioning the vehicle so as to select at least a second magnetic heading and repeating the obtaining, computing, and comparing steps for the at least second magnetic heading to provide at least one second calibration value for the heading system;

utilizing the first and the at least one second provided calibration values at the first and the at least one second magnetic headings of the vehicle to calculate a universal average gain and offset for the at least one magnetometer based on averaging the plurality of the first and the at least one second calibration values; and

utilizing the universal average gain and offset to universally calibrate the heading system with respect to measurement errors.

10. The heading system calibration method in accordance with claim 9 wherein the vehicle is a ship positioned in water along the Earth'"'"'s surface.

11. The heading system calibration method in accordance with claim 9 wherein the vehicle is selectively positioned to at least four different magnetic headings.

12. The method in accordance with claim 9 wherein the four different selected magnetic headings for the aircraft comprise the North, South, East, and West magnetic headings for the aircraft during the calibration.

13. The method in accordance with claim 9 further comprising:

utilizing at least one low pass filter to filter the calibration values of the plurality of magnetic headings for the positioned aircraft.