Triaxial Magnetometer Network for Magnetic Object Localization
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Solution Overview
Problem
Existing magnetic localization devices are imprecise and unstable due to measurement biases caused by the user's movement and changes in the Earth's magnetic field, making them unsuitable for mobile use, especially in applications requiring high accuracy like digitizing handwritten traces.
Innovation Solution
A method involving a network of triaxial magnetometers that calculates a weighted average of measurements to separate the Earth's magnetic field and the magnetic field of a moving object, allowing for precise localization while accounting for homogeneous magnetic fields and disturbances, enabling use in environments like trains or trams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a network of tri-axis magnetometers is used to locate a magnetic object, then location capability is provided, but measurement bias from Earth's magnetic field variations and device movement causes imprecision and instability
Solution Approach 1:
The patent segments the magnetic field measurement problem by separating the Earth's magnetic field component from the local magnetic field component. It uses a first magnetometer specifically to measure the Earth's magnetic field and a second magnetometer to measure the combined field, then processes these separate measurements to eliminate the bias. This segmentation allows the system to maintain precision while compensating for environmental variations and device movement.
Solution Approach 2:
The patent introduces an intermediary processing step that calculates the difference between the first magnetometer's measurement (Earth's field only) and the second magnetometer's measurement (combined field). This intermediary calculation serves as a mediator to eliminate the Earth's magnetic field bias from the location calculation, thereby improving measurement stability without sacrificing location capability.
2Ease of operation
If the device is moved to allow mobile use and changing writing angles, then ease of operation is improved, but measurement bias from Earth's magnetic field rotation increases, degrading location precision
Solution Approach 1:
The patent performs preliminary measurement of the Earth's magnetic field using the first magnetometer before using the second magnetometer to locate the magnetic object. By pre-measuring and storing the Earth's magnetic field characteristics, the system can later subtract this known bias from the combined field measurement, enabling accurate location even when the device is moved or oriented differently. This preliminary action maintains location precision while enabling mobile usability.
3Measurement precision
If a remote magnetometer is placed at sufficient distance to eliminate local magnetic field interference, then measurement bias from Earth's field is reduced, but device size increases and sensitivity to remote magnetometer errors increases
Solution Approach 1:
The patent applies local quality by assigning different functional roles to different parts of the device. The first magnetometer is positioned and configured specifically to measure the Earth's magnetic field with minimal local interference, while the second magnetometer is positioned to measure the combined field including the local magnetic object. This differentiated local functionality allows both magnetometers to be compact while performing their specific measurement tasks effectively, avoiding the need for a large distant remote magnetometer.
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 enables accurate determination of a mobile magnetic object's position and orientation, reducing measurement deviations and allowing for use during device movement, thereby improving the precision and reliability of magnetic localization systems.
Implementation Method 1
a network of at least N triaxial magnetometers mechanically linked together without any degree of freedom to maintain a position known relative of these magnetometers
Data Source
Figure 1~2
Figure 3
AI summary
Method for locating at least one movable magnetic object (OMMk) relative to a network of at least N triaxial magnetometers (Mi,j) comprising the steps consisting in: subtracting a weighted mean "Bmes" from each of said measurements (B i,j mes) to obtain modified measurements (B i,j mes-); inputting said modified measurements (B i,j mes-) and a location (Pos t, M t) of the one or more movable magnetic objects (OMM k) at the current instant (t) into a filtering operation (FL) for locating the one or more movable magnetic objects (OMM k); carrying out the locating filtering operation (FL), this operation comprising the steps consisting in: subtracting a weighted mean "B est" from each of said estimated data (B i,j est); and outputting a location (Pos t+1, M t+1) of the one or more movable magnetic objects (OMM k) at a following instant (t+1). Such a method allows, for example, a stylus moved above an electronic device such as a tablet to be located magnetically while removing the contribution of the Earth's magnetic field or other parasitic fields by averaging the measurements originating from said magnetometers.