Multi-pole Magnet Angular Sensor for External Field Immunity
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Solution Overview
Problem
Existing position sensors using magnetic fields for angular measurement are sensitive to external magnetic fields and require additional shielding or robustness, especially in applications like automotive systems where large currents generate significant disturbance fields, and they are not effective for measuring angles less than 360° with high sensitivity.
Innovation Solution
A contactless arrangement using a multi-pole magnet with at least four poles and a sensor with multiple Hall effect elements partitioned into groups to measure tangential, radial, and axial magnetic field components, providing a robust and sensitive method for determining angular position that is insensitive to external fields and position-offset errors, without the need for ferromagnetic shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a two-pole magnet with horizontal Hall elements is used to subtract external fields, then external field immunity is improved, but measurement sensitivity for small angles deteriorates
Solution Approach 1:
The patent applies asymmetry by using a multi-pole magnet configuration (at least four poles) arranged asymmetrically relative to the sensor elements. This asymmetric arrangement creates a magnetic field pattern where the tangential component varies significantly with small angular changes, thereby improving small angle measurement sensitivity while maintaining external field rejection through the symmetric cancellation mechanism of diametrically opposed sensor elements.
Solution Approach 2:
The patent transitions from measuring only axial field components (Bz) to measuring tangential field components (Bt) in addition to radial components (Br). This dimensional change in measurement approach allows the sensor to exploit the tangential field variation that occurs with small angular displacements, thereby improving sensitivity while the differential measurement technique continues to reject external fields.
2Object-affected harmful factors
If ferromagnetic shielding is used to protect against external magnetic fields, then external field immunity is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical ferromagnetic shielding approach with a field-based solution. By using a multi-pole magnet configuration and measuring tangential field components, the system achieves external field immunity through electromagnetic field manipulation and differential measurement techniques, eliminating the need for additional ferromagnetic shield structures.
Solution Approach 2:
The measurement system itself provides the external field rejection capability through its inherent multi-pole configuration and differential measurement technique. The system uses its own magnetic field structure and sensor arrangement to cancel external field effects, making the shielding function self-contained within the measurement mechanism rather than requiring separate protective structures.
3Measurement precision
If a multi-pole magnet with at least four poles is used, then small angle measurement sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple functional requirements into a single multi-pole magnet structure. The same magnet that generates the magnetic field for measurement also provides the asymmetric field pattern necessary for small angle sensitivity and the symmetric pattern necessary for external field rejection. This consolidation achieves multiple objectives without proportionally increasing device complexity.
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 offers high sensitivity and accuracy for angular position measurement, particularly for angles less than 360°, while being robust to external magnetic fields and position-offset errors, making it suitable for harsh environments like automotive applications.
Implementation Method 1
A contactless arrangement using a multi-pole magnet with at least four poles and a sensor with multiple Hall effect elements partitioned into groups to measure tangential, radial, and axial magnetic field components
Data Source
AI summary
A system for measuring an angular position of a rotor with respect to a stator, wherein the rotor is rotatable around a rotation axis, and the system includes: a magnetic source mounted on the rotor, having at least four magnet poles and providing a periodically repetitive magnetic field pattern with respect to the rotation axis; a sensor mounted on the stator and comprising a plurality of sensor elements for measuring at least one magnetic field component of the magnetic field and for providing a measurement signal thereof; the sensor being located substantially centered around the rotation axis, in a plane substantially perpendicular to the rotation axis at a first distance from the magnetic source; the sensor elements being located substantially on a circle at a second distance from the rotation axis; a calculator that determines the angular position by calculating it from the measurement signals.