Magnet Sensor Assembly Position Sensing Under External Field Noise
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Solution Overview
Problem
Existing methods for determining the position of a magnet using magnetic field sensors are prone to errors due to signal noise and external magnetic fields, leading to distorted measurements and poor signal-to-noise ratios.
Innovation Solution
A method involving a magnet-sensor arrangement with at least one sensor pair, where magnetic flux densities are measured, non-differentially and differentially calculated, normalized, and weighted to minimize the impact of external fields while maintaining a favorable signal-to-noise ratio, using trigonometric functions and multi-point calibration for precise position determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the magnetic field measurement is performed using a single sensor, then the signal-to-noise ratio is good, but the measurement is distorted by external magnetic fields
Solution Approach 1:
The measurement system is divided into multiple sensors arranged in a specific geometry (e.g., three sensors in a triangular arrangement). Each sensor provides an independent measurement of the magnetic field, and the final position is determined by combining these segmented measurements through a centroid calculation, thereby achieving both external field immunity and good signal-to-noise ratio
Solution Approach 2:
The patent combines the output signals from multiple sensors through a weighted averaging process. The centroid position is calculated by merging the individual sensor measurements, where each sensor's contribution is weighted by its signal strength. This merging process maintains the signal-to-noise ratio while providing immunity to external fields that affect all sensors equally
2Reliability
If multiple sensors are used to factor out extraneous fields by calculating differences, then extraneous field immunity is achieved, but the signals are significantly attenuated and noise is significantly amplified
Solution Approach 1:
Instead of calculating differences between sensor signals (which attenuates the signal and amplifies noise), the patent inverts the approach by calculating a weighted sum or centroid of the sensor signals. This inversion maintains the beneficial extraneous field immunity while preserving the signal strength and avoiding noise amplification
Solution Approach 2:
The patent changes the calculation parameter from difference-based (which causes signal attenuation) to centroid-based weighted averaging (which preserves signal strength). By changing the mathematical operation from subtraction to weighted summation, the system achieves extraneous field immunity without the detrimental effects of signal attenuation and noise amplification
3Measurement precision
If absolutely measured signals are used without subtraction, then the signal-to-noise ratio is good, but the extraneous field distorts the measurement results significantly
Solution Approach 1:
The patent introduces an intermediary calculation step where the individual sensor measurements are first processed to determine a centroid position. This intermediary centroid calculation acts as a mediator that combines the good signal-to-noise ratio of absolute measurements with the extraneous field immunity of differential measurements, without requiring actual signal subtraction
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
The method provides accurate magnet position determination with immunity to external fields and improved signal-to-noise ratio, enabling precise feedback and control without mechanical detents.
Implementation Method 1
a magnet, in particular a permanent or electromagnet, which is usually located on the control element, and at least one sensor capable of determining the magnetic field
Data Source
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AI summary
A method for signal processing from a magnet-sensor arrangement (1), wherein the magnet-sensor arrangement (1) comprises at least one sensor pair (3) and a magnet (2) movably mounted thereon, comprising the following steps: measuring the magnetic flux density per spatial coordinate per sensor; calculating a non-differential change in the position of the magnet (2) for each magnetic flux density measured in step a); calculating the differences of the measured magnetic flux densities per spatial coordinate; calculating a differentially calculated change in the position of the magnet (2) from the magnetic flux densities calculated in step c); normalizing the non-differentially and differentially calculated changes in the position of the magnet (2) based on a zero position of the magnet (2); calculating the differences between the differentially calculated change in the position of the magnet (2) and the non-differentially calculated changes in the position of the magnet (2);Calculate a weighting factor based on the differences calculated in step f); calculate a mean value, weighted by the weighting factor from step g), of the non-differential and differentially calculated position changes of the magnet (2) normalized in step e) in order to obtain a corrected position change.