Magnetic Position Sensor Angular Accuracy via Field Cancellation

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Solution Overview

Problem

Existing magnetic position sensors face challenges in accurately determining the angular position over time due to sensitivity mismatch between sensing elements caused by ageing effects, which affects the accuracy of magnetic field measurements.

Innovation Solution

The method involves generating local magnetic fields by applying currents to conductors or coils near sensing elements to reduce or cancel out the external magnetic field, allowing for accurate calculation of the angular position independent of sensitivity drift, using a combination of Hall and magneto-resistive elements and control loops to adjust currents and minimize total magnetic field amplitudes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If magnetic field measurements are taken using existing sensors over time, then position data can be obtained, but sensitivity mismatch between sensing elements occurs due to ageing effects, degrading measurement accuracy

Engineering Contradiction:

Improveangular position measurement accuracyVSAvoidlong-term stability against ageing

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the measurement parameter from direct magnetic field strength to magnetic field direction (angle). By measuring the angle of the magnetic field vector rather than its magnitude, the system becomes insensitive to ageing-related sensitivity drift in the sensing elements, as directional information remains stable even when sensitivity changes

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of sensitivity mismatch into a beneficial feature by using it to determine field direction. The ratio of measurements from sensing elements with different sensitivities naturally provides directional information that is independent of absolute sensitivity values, turning the ageing problem into a robust solution

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If multiple sensing elements are used to improve measurement robustness, then resistance to external magnetic fields and position errors increases, but sensitivity mismatch between elements due to ageing still affects accuracy

Engineering Contradiction:

Improverobustness against external magnetic fields and position errorsVSAvoidangular position accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

Instead of using multiple sensing elements to measure field strength and averaging or comparing magnitudes, the patent inverts the approach by using the same multiple elements to determine field direction through angular measurement. The calculation focuses on the angle of the magnetic field vector rather than the magnitude, making the system robust to both external fields and ageing effects simultaneously

Inventive Principle:

Principle #13The other way round (Inversion)

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 approach reduces the impact of sensitivity mismatch due to ageing, enabling precise and stable angular position determination by maintaining the total magnetic field at or below predefined thresholds, thus improving long-term accuracy and reliability.

Implementation Method 1

applying or adjusting a first current to a first electrical conductor to generate a first internal magnetic field that will superimpose with the external magnetic field

Methodology Applied

Scientific EffectElectromagnetic field generation: Electromagnetic Induction

Implementation Method 2

measuring a component of the first total magnetic field at a first location using a first magnetic sensing element

Methodology Applied

Scientific EffectMagnetic field sensing: Hall Effect

Implementation Method 3

applying or adjusting a second current to a second electrical conductor different from the first electrical conductor to generate a second internal magnetic field that will superimpose with the external magnetic field

Methodology Applied

Scientific EffectElectromagnetic field generation: Electromagnetic Induction

Implementation Method 4

measuring a component of the second total magnetic field at a second location using a second magnetic sensing element different from the first magnetic sensing element

Methodology Applied

Scientific EffectMagnetic field sensing: Hall Effect

Data Source

PatentUS10415997B2Position sensor and method of position sensing

Publication Date: 2019.09.17 MELEXIS TECHNOLOGIES SA

AI summary

A method of determining a position of a sensor device relative to an external magnetic field, comprises: providing currents to conductors to generate an internal magnetic field that will superimpose with the external magnetic field, measuring field components of the combined magnetic field, calculating a position based on the applied currents and/or on the measured residual magnetic field. A position sensor is provided for performing the method.