Magnetic Compass Calibration on Unstable Platforms
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Solution Overview
Problem
Magnetic compass calibration is challenged by unstable platforms, dynamic conditions, and local distortions in the magnetic field, such as those caused by nearby magnetic minerals or solar activity, which affect the accuracy of magnetic north determination and transformation of measurements between coordinate systems.
Innovation Solution
A method and system for calibrating magnetic compasses that involve receiving sample data from multiple orientations, estimating calibration coefficients using iterative least squares minimization, and weighting stored calibration components based on observability, to determine a sensor-orientation-independent magnetic field vector, accounting for hard and soft iron effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration is performed using traditional methods on unstable platforms, then calibration can be completed, but calibration accuracy is reduced
Solution Approach 1:
The system performs preliminary actions by storing calibration components from multiple orientations in advance, then uses these pre-stored components during actual calibration to compensate for platform instability, allowing accurate calibration even when the platform moves during the calibration process
Solution Approach 2:
The system uses feedback by iteratively estimating calibration coefficients and comparing them against stored calibration components, adjusting the estimates based on the comparison until convergence is achieved, thereby improving calibration accuracy despite platform instability
2Ease of operation
If calibration samples are collected at limited orientations, then calibration process is simplified, but calibration accuracy over unsampled orientations deteriorates
Solution Approach 1:
The system performs preliminary action by pre-storing calibration components collected from multiple orientations before actual use. This allows the system to maintain calibration accuracy across all orientations including unsampled ones, without requiring complex real-time data collection during operation
Solution Approach 2:
The stored calibration components serve multiple functions: they can be used for calibration at sampled orientations, provide accuracy at unsampled orientations, and enable operation on unstable platforms. This multi-functionality resolves the contradiction between simplicity and accuracy
3Measurement precision
If local magnetic field distortions are present, then magnetic field measurements are affected, but the distortions cannot be eliminated
Solution Approach 1:
The system converts the harmful effect of local magnetic field distortions into a beneficial calibration target. By storing calibration components that capture the distorted field characteristics and using them to estimate calibration coefficients, the system compensates for the distortions and achieves accurate measurements despite their presence
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
The solution improves calibration accuracy over sampled orientations and maintains it over unsampled orientations, providing better post-calibration compass accuracy and reducing the impact of dynamic conditions and local distortions.
Implementation Method 1
A magnetometer senses and provides information regarding magnetic fields
Implementation Method 2
An accelerometer senses and provides information regarding acceleration
Data Source
AI summary
A system and method of determining a magnetic field and magnetic compass calibration is disclosed. One embodiment is a method of determining a magnetic field vector, the method comprising storing, for each of a plurality of sensor orientations, one or more calibration components, determining, for a sensor orientation not included in the plurality of sensor orientations, a magnetic field vector and a gravity vector, iteratively estimating one or more calibration coefficients based on the stored components, the determined magnetic field vector, and the determined gravity vector, wherein the calibration coefficients are updated during each of a plurality of iterations, and determining a sensor-orientation-independent magnetic field vector based on at least one of the calibration coefficients.