Three-Axis Magnetometer Calibration Using Sensor Fusion
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Solution Overview
Problem
Current techniques for calibrating three-axis magnetometers in electronic devices face inefficiencies, including incomplete determination of soft iron matrix coefficients, requirement of zero translational acceleration, and continuous spatial attitude determination, which hinder accurate magnetic heading and attitude determination.
Innovation Solution
A calibration method that co-processes measurements from a three-axis magnetometer, accelerometer, and gyroscope to determine both hard and soft iron errors without external assistance, using geographic coordinates to calculate magnetic declination and convert magnetic heading, and employing a three-stage calibration process to isolate and correct internal magnetic field components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current calibration techniques are used, then magnetic heading determination can be achieved, but the calibration process requires zero translational acceleration and continuous spatial attitude determination which reduces efficiency
Solution Approach 1:
The calibration process is divided into three distinct stages: (1) determining hard iron error parameters, (2) determining soft iron error parameters, and (3) determining misalignment error parameters. This segmentation allows each stage to focus on specific error types with tailored measurement requirements, eliminating the need for continuous attitude determination throughout the entire process and improving calibration efficiency.
Solution Approach 2:
The method performs preliminary actions by first determining hard iron error parameters before proceeding to soft iron error parameters, and finally misalignment errors. This preliminary structuring of the calibration process allows each subsequent stage to build upon previously established corrections, reducing the complexity and requirements of later stages while maintaining measurement precision.
2Measurement precision
If current calibration techniques are used, then soft iron matrix coefficients can be determined, but the process does not determine the entire set of soft iron coefficients which limits calibration completeness
Solution Approach 1:
The method transitions from two-dimensional magnetometer measurements to three-dimensional calibration by incorporating accelerometer data and performing measurements along three orthogonal axes. This dimensional expansion enables determination of the complete 3x3 soft iron matrix coefficients rather than partial coefficients, achieving full calibration parameter completeness.
Solution Approach 2:
The accelerometer serves as an intermediary device that provides gravitational reference information to complement magnetometer measurements. By combining data from both sensors, the system can determine complete soft iron error parameters without relying solely on magnetometer data, which would be insufficient for full coefficient determination.
3Ease of operation
If three-axis magnetometer is rigidly fixed in housing, then sensor orientation relative to housing is fixed, but internal magnetic field components cause systematic errors in measurements
Solution Approach 1:
The calibration method enables the magnetometer system to self-correct for internal magnetic field distortions by determining hard iron, soft iron, and misalignment error parameters through automated measurement and calculation processes. This self-service calibration eliminates the need for manual intervention or complex mounting arrangements while restoring measurement accuracy.
Solution Approach 2:
The method changes the approach from physically adjusting sensor mounting to mathematically correcting measurement parameters. By determining and applying correction parameters for hard iron, soft iron, and misalignment errors, the system compensates for internal magnetic field effects without requiring changes to the physical sensor mounting configuration.
Data Source
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AI summary
A method and device for calibration of a three-axis magnetometer that facilitates a more efficient and routine procedure by calibration of hard and soft iron errors of a 3D-magnetometer integrated into a mobile electronic device, and a set of operations for coprocessing measurements of the 3D-magnetometer and inertial sensors (e.g., a 3D-accelerometer and 3D-gyro), which can determine magnetic heading and attitude of the electronic device.