Magnetometer Calibration Using Inertial Data
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Solution Overview
Problem
Existing methods for calibrating magnetometers on moving objects, such as vehicles, face challenges due to non-homogeneous and non-stationary ambient magnetic fields, which are affected by nearby metal objects and the object's own magnetic properties, leading to errors and the need for frequent recalibrations.
Innovation Solution
A method that acquires magnetic field components and angular velocity using magnetometers and inertial measurement units, processing data to determine calibration parameters by minimizing expressions related to estimated magnetic field components and equations, distinguishing between errors and external disturbances, and recursively filtering or optimizing to achieve accurate calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetometers are calibrated using traditional methods assuming homogeneous and stationary magnetic fields, then calibration can be performed, but the calibration becomes inaccurate and requires frequent recalibration due to non-homogeneous and non-stationary ambient magnetic fields
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors the consistency between magnetometer measurements and gyroscope-based attitude predictions. When discrepancies are detected, the system identifies and corrects calibration errors, creating a closed-loop calibration process that adapts to changing magnetic conditions and maintains high measurement precision without frequent recalibration.
Solution Approach 2:
The patent replaces traditional mechanical calibration methods (which require physical rotation of the sensor in controlled environments) with a computational approach that uses the relationship between magnetometer measurements and gyroscope data to derive calibration parameters algorithmically, enabling calibration in operational environments without mechanical constraints.
2Adaptability or versatility
If the magnetometer is mounted on a vehicle, then the magnetometer can measure magnetic field in the vehicle's reference frame, but the calibration becomes invalid when the vehicle changes orientation, loads, or magnetic properties
Solution Approach 1:
The patent implements dynamic calibration that adapts to changing vehicle conditions in real-time. The system continuously updates calibration parameters based on the current relationship between magnetometer measurements and gyroscope-based attitude estimates, allowing the calibration to remain valid despite changes in vehicle orientation, loading, or magnetic properties.
Solution Approach 2:
The patent creates a universal calibration method that works across different vehicle conditions and orientations by using the fundamental relationship between magnetic field measurements and rotational motion. The calibration approach is not tied to specific vehicle configurations but rather adapts to any operational state through the feedback mechanism.
3Measurement precision
If high-precision sensors are used for navigation, then measurement accuracy improves, but the sensors become expensive, heavy, and bulky
Solution Approach 1:
The patent creates a computational copy or model of the magnetic field and attitude relationships that replaces the need for expensive high-precision sensors. By using algorithmic calibration that processes data from standard sensors, the system achieves navigation precision without requiring heavy, expensive high-precision hardware.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides reliable and efficient calibration of magnetometers, reducing errors and the need for frequent recalibrations, allowing for precise movement estimation and navigation in varying magnetic environments.
Implementation Method 1
Acquisition by magnetometers of at least three measured components of the magnetic field at the magnetometers
Implementation Method 2
by inertial measuring means attached to said object, of an angular velocity of the object
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method for calibrating magnetometers (20) that are fitted in an object (1) moving in an ambient magnetic field, said method being characterized in that it involves the steps of: (a) having the magnetometers (20) acquire at least three measured components of the magnetic field around the magnetometers (20), and having inertial measurement means (11), which are secured to the object (1), acquire an angular velocity of the object (1); (c) having data processing means (21) determine values of at least one calibration parameter of the magnetometers (20), said values minimizing an expression defined by estimated components of the magnetic field, and at least one magnetic equation relating to the angular velocity of the object (1), - the estimated components of the magnetic field being a function of the measured components of the magnetic field as well as of calibration parameters of the magnetometers (20), and - the at least one magnetic equation assuming that the magnetic field is uniform and stationary around the magnetic measurement means (20).