Ellipsoid-Based Magnetic Interference Compensation for Magnetometers

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Solution Overview

Problem

Magnetic sensors in portable devices are adversely affected by 'hard-iron' and 'soft-iron' interferences, leading to errors in magnetic field readings, which compromise navigational and orientation functionalities.

Innovation Solution

The implementation of a processor, potentially a field-programmable gate array, that calculates parameters of an ellipsoid to compensate for magnetic field data, allowing for offset and recovery calibration parameters to be applied, effectively transforming measured magnetic field data to cancel out interference, thereby improving sensing accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If magnetic field sensing is performed in portable devices, then navigational and orientation functionality is provided, but hard-iron and soft-iron interferences induce errors in magnetometer readings

Engineering Contradiction:

Improvemagnetic field sensing accuracyVSAvoidhard-iron and soft-iron interferences

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by performing calibration procedures before actual magnetic field measurements. The system pre-determines correction parameters (offset and scaling factors) by exposing the magnetometer to known magnetic field conditions and storing these calibration data for later use in compensating measurement errors

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the measured magnetic field data to continuously refine and update calibration parameters. The system monitors measurement deviations and adjusts compensation parameters accordingly, creating a closed-loop system that improves measurement accuracy over time

Inventive Principle:

Principle #23Feedback

2Measurement precision

If calibration parameters are calculated and applied to compensate for magnetic interference, then sensing accuracy is improved, but device complexity increases due to additional processing requirements

Engineering Contradiction:

Improvemagnetic field measurement accuracyVSAvoidprocessor computation requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by transforming the magnetic field measurement data through mathematical operations (rotation matrices, scaling transformations) to correct for interference. Instead of modifying the physical sensor, the system changes the parameters of the measured data to compensate for hard-iron and soft-iron effects

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces mechanical or physical compensation methods with computational algorithms. Rather than using additional physical sensors or mechanical adjustment mechanisms, the system uses software-based calibration and compensation algorithms to achieve the same goal of improving measurement accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9506755B2Compensating magnetic interference for electronic magnetometer sensors

Publication Date: 2016.11.29 STMICROELECTRONICS CHINA INVESTMENT

AI summary

Apparatus and methods to compensate hard iron and soft iron magnetic interference in magnetic sensing devices are described. Hard and soft iron interference may be modeled using an ellipsoidal surface generated by a plurality of magnetic field measurements. A displacement of the ellipsoid from a reference frame origin corresponds to hard iron or permanent magnetic field interference. A shape and orientation of the ellipsoid corresponds to soft iron magnetic field interference. The ellipsoidal surface may be analyzed to obtain magnetic field compensation values for cancelling hard iron and soft iron interference.