EMT Tracking Using Inertial Data to Resolve Ambiguities

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Solution Overview

Problem

Electromagnetic Tracking (EMT) systems face ambiguities in determining the position and orientation of objects in complex magnetic fields, particularly due to phase-lock loop (PLL) and hemisphere ambiguities, which require initial calibration and can be disrupted by faults like communication failures.

Innovation Solution

Incorporating an inertial measurement unit (IMU) to provide inertial data, which resolves PLL and hemisphere ambiguities by correlating measured angular and linear velocities with estimated values, allowing self-calibration and fault recovery without initial position or orientation confirmation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If electromagnetic tracking systems use phase-lock loop and hemisphere ambiguity resolution methods, then position and orientation determination becomes possible, but initial calibration is required and system reliability decreases due to vulnerability to communication failures

Engineering Contradiction:

Improveposition and orientation determinationVSAvoidsystem reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces an inertial measurement unit (IMU) as an intermediary device that provides independent motion data to resolve ambiguities in electromagnetic tracking. The IMU acts as a mediator between the electromagnetic field measurements and the final position/orientation determination, allowing the system to resolve PLL and hemisphere ambiguities without relying on vulnerable communication channels or initial calibration states.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If electromagnetic tracking systems require initial calibration to resolve ambiguities, then measurement precision can be achieved, but loss of time occurs during calibration and startup

Engineering Contradiction:

Improveposition and orientation accuracyVSAvoidcalibration time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent implements preliminary action by continuously collecting and processing inertial measurement data in advance, building up a repository of motion characteristics before electromagnetic tracking begins. This pre-collected inertial data is then used to immediately resolve ambiguities when tracking starts, eliminating the need for time-consuming initial calibration procedures.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system performs self-service by using its own inertial measurement capabilities to autonomously resolve ambiguities without requiring external calibration inputs or manual setup. The IMU provides self-contained motion reference data that enables the electromagnetic tracking system to independently determine its own position and orientation accuracy.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If electromagnetic tracking systems operate in complex magnetic fields, then tracking capability is provided, but measurement precision deteriorates due to PLL and hemisphere ambiguities

Engineering Contradiction:

Improvetracking capabilityVSAvoidposition and orientation accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent merges electromagnetic field measurements with inertial measurement data to create a hybrid tracking system. By combining the positional information from electromagnetic fields with the motion reference data from the IMU, the system maintains tracking capability in complex magnetic fields while the inertial data provides the additional constraints needed to resolve ambiguities and maintain precision.

Inventive Principle:

Principle #5Merging (Combining)

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

Enables accurate and autonomous tracking of objects in EMT systems, eliminating the need for initial calibration and facilitating system recovery from faults, thereby improving reliability and efficiency in applications like medical and VR settings.

Implementation Method 1

The inertial data can include linear acceleration data measured by one or more accelerometers. The inertial data can include angular velocity data provided by one or more gyroscopes.

Methodology Applied

Scientific EffectInertial measurement: Accelerometer

Data Source

PatentUS10539644B1Tracking an object in an electromagnetic field

Publication Date: 2020.01.21 NORTHERN DIGITAL

AI summary

An electromagnetic tracking (EMT) system includes a tracked device, a tracking device, and a computing device. The EMT system is configured to receive, at the tracking device, an electromagnetic signal generated by the tracked device, determine, based on the electromagnetic signal, a set of possible positions and orientations of the tracked device relative to the tracking device, receive a measured inertial value representing a motion of the tracked device, determine an estimated inertial value corresponding to the motion of the tracked device based on at least one position and orientation of the set of possible positions and orientations, determine a difference value representing a difference between the estimated inertial value and the measured inertial value, determine a particular position and a particular orientation from the set in response to determining the difference value, and generate an output including the particular position and particular orientation.