2D Magnetometer Calibration for Heading Accuracy
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Solution Overview
Problem
Existing nine-axis sensors in electronic devices face challenges in fully exploiting their capabilities due to difficulties in calibrating and removing undesirable effects from gyroscope zero-rate offset, magnetometer noise, and interference, particularly in applications with limited motion, such as robotic vacuum cleaners and devices mounted in cars.
Innovation Solution
A method for determining heading using a 2D magnetometer calibration technique that fits the magnetic field data to a circle, ellipse, or skewed ellipse, and combines it with sensor fusion algorithms to correct for soft-iron and hard-iron effects, utilizing gyroscope data to enhance calibration accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 3D magnetometer calibration is used, then calibration accuracy can be achieved in free motion, but calibration fails or becomes inaccurate in constrained motion scenarios
Solution Approach 1:
The patent changes the calibration model parameters by transitioning from 3D ellipsoid fitting to 2D circle/ellipse fitting. This parameter change adapts the calibration approach to constrained motion scenarios where the magnetometer is restricted to moving within a plane, allowing accurate calibration without requiring full 3D motion freedom.
Solution Approach 2:
The patent segments the calibration problem by separating the 3D calibration into 2D calibration. By dividing the calibration space from three dimensions to two dimensions, the method makes calibration feasible and accurate for devices with constrained motion, such as robotic vacuum cleaners and car-mounted devices.
2Adaptability or versatility
If nine-axis sensors are used, then enhanced functionality is provided, but calibration difficulty and error removal complexity increase
Solution Approach 1:
The patent extracts and addresses specific error sources (hard-iron and soft-iron effects) separately through dedicated calibration procedures. By isolating these error components and developing targeted calibration methods, the system manages the complexity of nine-axis sensor calibration while maintaining enhanced functionality.
Solution Approach 2:
The patent performs preliminary calibration to establish baseline magnetometer accuracy before operation. By conducting calibration in advance, even in constrained motion scenarios, the system prepares the sensors to function accurately, reducing the complexity of real-time error correction during actual use.
3Ease of manufacture
If magnetometer calibration is performed without constrained motion consideration, then general calibration can be achieved, but accuracy deteriorates in applications with limited motion
Solution Approach 1:
The patent applies local quality by adapting the calibration approach to the specific motion constraints of the application. Instead of using a universal 3D calibration method, the system employs 2D calibration specifically tailored to constrained motion scenarios, improving accuracy where it matters most without compromising overall system generality.
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 method provides accurate heading determination even in constrained motion scenarios by effectively calibrating magnetometers, reducing errors from interference, and improving long-term stability through sensor fusion with gyroscopes and accelerometers.
Implementation Method 1
The magnetometers measure a local magnetic field vector (or a deviation thereof)
Implementation Method 2
The accelerometer senses gravity, and, hence, can be used to define the Z-axis
Implementation Method 3
The 3-D gyroscopes measure angular velocities
Data Source
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AI summary
Methods, apparatus, and systems directed to calibrating a magnetometer. Among such are methods that use only the horizontal components of magnetometer measurements. Then, planar calibrated magnetic field output measurements can be used in sensor fusion with data from gyroscope(s) and accelerometer(s). In other embodiments, heading information from the planar calibrated magnetic field is fused with the heading calculated from gyroscope integration. Other such methods include any of generating combined information including 6-axis fusion information and magnetometer information; accumulating values for any of a first matrix [T] and a first vector [U] according to the combined information; generating a second matrix [K] according to any of a pseudo-inverse of the first matrix [T] and the first vector [U]; generating any of a scale and skew matrix and an offset according to the first matrix [K]; and calibrating the magnetometer according to any of the scale and skew matrix and the offset.