Multipole Magnet Hall Sensor Stray Field Compensation
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Solution Overview
Problem
Existing systems for measuring rotation angles using X/Y Hall sensors and permanent magnets face interference from stray magnetic fields generated by current-carrying conductors, leading to inaccuracies in angle measurement due to the difficulty in compensating for these fields, especially in environments with numerous conductors like modern cars.
Innovation Solution
A multipole permanent magnet with four or more poles is rotatably mounted, generating a symmetrical magnetic field with two pairs of vertical Hall sensors positioned to ensure the sum of magnetic field vectors is zero, allowing the computation and subtraction of stray magnetic field components to improve angle measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall sensors are used to measure rotation angles in the presence of current-carrying conductors, then angle measurement can be performed, but measurement precision deteriorates due to stray magnetic fields
Solution Approach 1:
The system segments the magnetic field measurement by using multiple Hall sensors (at least three) positioned at different locations. Each sensor measures the magnetic field at its specific position, allowing the system to differentiate between the signal field from the multipole magnet and the stray magnetic field from external conductors through spatial analysis and mathematical processing.
Solution Approach 2:
The patent introduces mathematical processing and signal evaluation as an intermediary between the raw Hall sensor measurements and the final angle determination. The control device performs calculations that separate the stray magnetic field components from the signal field, effectively using computation as a mediator to eliminate interference.
2Measurement precision
If compensation methods are applied to stray magnetic fields, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The system changes parameters by using a multipole magnet with four or more poles instead of traditional two-pole magnets. This creates a magnetic field pattern with multiple alternating poles around the rotation axis, which when combined with strategically positioned Hall sensors, enables the system to identify and compensate for stray field effects through the specific spatial distribution of magnetic field measurements.
Solution Approach 2:
The system performs self-diagnosis and self-correction by using the measurements from multiple Hall sensors to automatically identify and compensate for stray magnetic field interference. The control device calculates the stray field components based on the sensor readings and subtracts them from the total measurement, allowing the system to correct its own errors without external intervention.
3Reliability
If shielding is applied to block stray magnetic fields, then measurement reliability improves, but ease of operation deteriorates due to impossible complete shielding in modern car environments
Solution Approach 1:
The patent replaces mechanical/physical shielding approaches with a field-based computational approach. Instead of trying to physically block stray magnetic fields with shields (which would be complex and difficult to implement completely in modern car environments), the system uses mathematical processing of magnetic field measurements to eliminate the effect of stray fields, substituting computational methods for physical barriers.
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 achieves a suppression of stray magnetic fields by ≥65 dB, reducing maximum angle errors to less than 0.5°, thereby enhancing the accuracy of rotation angle measurements.
Implementation Method 1
The contactless measurement of a rotation angle with the aid of the Hall effect is known in the art
Implementation Method 2
A multipole permanent magnet with four or more poles is rotatably mounted, generating a symmetrical magnetic field
Data Source
AI summary
An apparatus (10) for determining a stray magnetic field in the vicinity of a sensor is described. The apparatus (10) has a multipole permanent magnet (60) with four or more poles and an axis of rotation (70). The multipole permanent magnet (60) produces a magnetic field (65) with magnetic field vectors (67). Two vertical Hall sensors (40a and 40) are so arranged in two positions on a circular path (50) about the axis of rotation, such that the sum of the magnet field vectors (67) measured at the two positions is substantially zero.