Distortion-Immune Position Tracking via Frequency Extrapolation

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Solution Overview

Problem

Magnetic position tracking systems face significant challenges in accurately measuring object positions due to distortions caused by metallic, paramagnetic, or ferromagnetic objects, which induce eddy currents and other interference effects in the magnetic field.

Innovation Solution

The system employs frequency extrapolation by generating alternating current (AC) magnetic fields at multiple frequencies, sensing these fields, and extrapolating the data to a target frequency, such as zero or infinite frequency, to reduce distortion effects, allowing for accurate position calculations using equivalent direct current (DC) field strengths that are not affected by eddy currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If magnetic field measurements are performed in the presence of metallic or ferromagnetic objects, then position tracking can be performed, but measurement accuracy deteriorates due to field distortion and eddy currents

Engineering Contradiction:

Improveposition measurement accuracyVSAvoidfield distortion from metallic objects

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by measuring magnetic field signals at multiple different frequencies and then extrapolating to a target frequency (such as zero or infinite frequency) where distortion effects are minimized or eliminated. This frequency-domain parameter transformation allows the system to obtain distortion-free position measurements while operating in environments with metallic objects present.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of frequency-dependent distortion into a beneficial measurement approach by exploiting the fact that distortion varies predictably with frequency. By measuring at multiple frequencies and using extrapolation, the system transforms the presence of distorting objects from a problem into an opportunity to calculate and remove their effect, achieving accurate measurements even in challenging environments.

Inventive Principle:

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

2Measurement precision

If multiple frequency measurements are performed to compensate for distortion, then measurement accuracy improves, but measurement time and system complexity increase

Engineering Contradiction:

Improveposition measurement accuracyVSAvoidmeasurement time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies preliminary action by performing multiple frequency measurements and extrapolation calculations in advance, before final position determination is needed. The system pre-characterizes the distortion behavior at different frequencies and uses this pre-acquired data to quickly compute corrected position measurements, reducing real-time processing requirements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces direct single-frequency physical measurement with a computational approach using multiple frequency measurements and mathematical extrapolation. Instead of relying on a single physical measurement that would be distorted, the system substitutes a multi-frequency measurement and calculation process that mathematically eliminates distortion effects.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 effectively cancels out metal distortion effects, providing more accurate position tracking of objects relative to field generators, even in the presence of significant field-distorting materials, thereby improving the precision of magnetic position tracking systems.

Implementation Method 1

generating alternating current (AC) magnetic fields at two or more frequencies

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The distortion is sometimes caused by eddy currents that are induced in such objects by the system's magnetic field

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Implementation Method 3

extrapolating the dependence of the AC data points on the frequencies of the AC fields to a target frequency so as to determine the amplitudes and directions of the AC fields with a reduced level of the distortion

Methodology Applied

Scientific EffectFrequency extrapolation:

Data Source

PatentUS8326402B2Distortion-immune position tracking using frequency extrapolation

Publication Date: 2012.12.04 BIOSENSE WEBSTER INC

AI summary

A method for tracking a position of an object includes generating alternating current (AC) magnetic fields at two or more frequencies in a vicinity of the object using at least one field generator. The AC fields are sensed using a field sensor associated with the object. Corresponding AC data points that are indicative of amplitudes and directions of the AC fields at the field sensor are produced, wherein at least some of the sensed AC fields are subject to a distortion. A dependence of the AC data points on the frequencies of the AC fields is extrapolated to a target frequency so as to determine the amplitudes and directions of the AC fields with a reduced level of the distortion. Position coordinates of the object relative to the at least one field generator are calculated responsively to the extrapolated data points.