Linear Magnetic Position Sensor Circuit for Extended Stroke Sensing
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Solution Overview
Problem
Existing linear magnetic position sensors are limited in output range due to measurement ambiguities caused by external perturbation fields, requiring displacement constraints to avoid position derivation errors.
Innovation Solution
A linear magnetic position sensor circuit that computes a gradient magnitude value from first and second magnetic field components, comparing it to predetermined thresholds to output position signals based on sensing signal ratios or stored values, extending the output range while maintaining stray field immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If differential sensing is applied to reduce stray field effects, then stray field immunity is improved, but the measurable displacement range is limited due to modulo 2π jumps
Solution Approach 1:
The patent applies dynamics by making the processing method adaptive based on operating conditions. The system dynamically switches between two different position determination methods: using atan(ΔBx/ΔBz) when the magnet is within the linear range, and using a monotonic function of gradient magnitudes when approaching stroke ends. This dynamic adaptation resolves the contradiction by allowing the system to maintain both stray field immunity (through differential sensing) and extended measurable range (through method switching).
Solution Approach 2:
The patent changes the mathematical parameters used for position calculation based on the magnet's position. Instead of using a single fixed formula, the system transitions from using the angle atan(ΔBx/ΔBz) to using the ratio of gradient magnitudes |dBx/dx| and |dBz/dx|. This parameter change allows the system to overcome the modulo 2π limitation and achieve monotonic output across the entire stroke range while maintaining differential sensing for stray field rejection.
2Measurement precision
If the magnet displacement is limited to avoid modulo 2π jumps, then measurement unambiguity is maintained, but the output range is restricted
Solution Approach 1:
The patent segments the measurement range into two distinct zones: a linear range where atan(ΔBx/ΔBz) provides unambiguous position determination, and end zones where a monotonic function of gradient magnitudes is used. By dividing the overall measurement space and applying different methods to different segments, the system maintains measurement unambiguity in each segment while extending the total output range across the entire stroke.
Solution Approach 2:
The patent introduces an intermediary switching mechanism that selects between two different position calculation methods based on the current operating conditions. This intermediary (the switching logic that monitors gradient magnitudes and selects appropriate calculation methods) allows the system to transition smoothly between methods, maintaining unambiguous position determination while extending the overall measurable range beyond what a single method could achieve.
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 solution provides an extended output range with unambiguous position determination by using gradient magnitude comparisons and threshold-based signal output, ensuring reliable operation even in the presence of external magnetic interference.
Implementation Method 1
measuring the strength of a magnetic field generated by one or more magnet(s) at various locations, the position or orientation of the magnet(s) relative to the sensor elements can be determined
Data Source
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AI summary
The present invention relates to a linear magnetic position sensor circuit comprising : - at least one first sensor arranged to generate a first sensing signal indicative of a first magnetic field gradient of a first magnetic field component oriented in a first direction; - at least one second sensor arranged to generate a second sensing signal indicative of a second magnetic field gradient of a second magnetic field component oriented in a second direction different from the first direction; - processing circuit arranged to compute a gradient magnitude value based on said first and said second sensing signal and comprising comparison means for comparing said magnitude value to a first predetermined value. The processing circuit is further arranged to output a position signal based on a ratio of the first and the second sensing signal if the magnitude value is higher than the first predetermined value and to output a position signal based on a predetermined stored value and/or based on a function of said magnitude value if said magnitude value is lower than the first predetermined value.