Magnetometer Bias Correction for Mobile Object Location
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Solution Overview
Problem
Existing methods for locating a mobile magnetic object using a network of tri-axis magnetometers suffer from precision loss and algorithm divergence due to measurement biases and magnetization phenomena, especially when subjected to strong magnetic fields or ferromagnetic materials, which are not adequately accounted for over time.
Innovation Solution
A method that continuously detects and corrects for magnetometer magnetization by applying bias correction vectors to the measurements, limiting the influence of magnetized sensors in location filtering, and considering them as non-magnetizable, thereby improving accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetometers are used to locate mobile magnetic objects, then location capability is provided, but measurement biases and magnetization phenomena degrade precision and cause algorithm divergence
Solution Approach 1:
The patent applies preliminary action by detecting magnetized magnetometers before they significantly degrade measurement quality. The system continuously monitors magnetometer status and identifies magnetized sensors in advance, allowing corrective action (exclusion or recalibration) to be taken before the magnetization causes severe precision loss or algorithm divergence.
Solution Approach 2:
The patent implements feedback by continuously monitoring magnetometer measurements and comparing them against expected values. When a magnetometer shows signs of magnetization (deviations from expected measurement patterns), the system provides feedback to exclude or recalibrate that sensor, thereby maintaining overall system precision and reliability through closed-loop control.
2Measurement precision
If initialization bias correction is applied at start-up, then initial measurement biases are compensated, but magnetization biases that develop over time are not accounted for
Solution Approach 1:
The patent applies continuity of useful action by transitioning from a one-time initialization bias correction to continuous monitoring and detection of magnetized magnetometers throughout the device's operational lifetime. This ensures that precision maintenance is an ongoing process rather than a one-time event, extending reliable device usability indefinitely.
Solution Approach 2:
The system performs preliminary detection of magnetized magnetometers at regular intervals during operation, identifying sensors that have become magnetized before they significantly impact measurement quality. This allows for timely corrective action to maintain precision over the long term.
3Use of energy by moving object
If strong magnetic fields are used for localization, then signal strength increases, but magnetometer performance deteriorates due to saturation and magnetization
Solution Approach 1:
The patent applies partial action by using only the subset of magnetometers that are not magnetized or saturated. When some magnetometers are affected by strong magnetic fields, the system selectively excludes those sensors and relies on the remaining functional ones, thereby maintaining acceptable performance without requiring reduction of the magnetic field strength.
Solution Approach 2:
The system dynamically changes the operational status parameter of magnetometers based on their measured performance. When a magnetometer shows signs of saturation or magnetization, its status changes from active to excluded, allowing the system to adapt to varying magnetic field conditions and maintain precision despite the presence of strong fields.
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 enhances the precision and reliability of locating a mobile magnetic object by continuously accounting for magnetometer biases and magnetization effects, reducing estimation errors and extending device usability over time.
Implementation Method 1
a network of at least N triaxial magnetometers mechanically linked together without any degree of freedom to maintain a known relative position of these magnetometers
Implementation Method 2
locating at least one mobile magnetic object with respect to a network of at least N triaxial magnetometers
Data Source
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AI summary
This method for locating at least one movable magnetic object (OMMk) relative to a network of at least N triaxial magnetometers (Mi,j) that are connected to one another mechanically with no degree of freedom in order to preserve a known relative position of these magnetometers (Mi,j), N being an integer at least equal to 2, comprises, continuously: a step of detecting (E1) a magnetometer (M i, j) capable of being magnetized, i.e. capable of delivering as output measurements (B i,j mes) comprising a measurement bias (BM i,j mes) following a magnetization; a step (E2) of correcting, by means of a correcting bias (BC i,j mes), the measurements (B i,j mes) delivered by said magnetometer (M i, j) capable of being magnetized, said correcting bias (BC i,j mes) corresponding to a deviation between the measurements (B i,j mes) inputted by said magnetometer (M i, j) into a locating filtering operation (FL) and the estimations (B i,j est), during said locating filtering operation (FL), of the data delivered by said magnetometer (M i, j); and a step (E3) of considering said magnetometer (M i,j) as not capable of being magnetized, by taking into account said step of correcting said magnetometer (M i,j) capable of being magnetized. Such a process for example allows a magnetic object such as a stylus moved above an electronic device such as a tablet to be located while detecting when a magnetometer has an excessively high magnetization resulting in saturation of said magnetometer and while correcting for the effect of such a saturation on the location measurements.