Angular Sensor Stray Field Cancellation via Saturation Mode
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Solution Overview
Problem
Magnetic field sensors used for measuring angular position face inaccuracies due to the presence of stray magnetic fields, which cannot be distinguished from the actual rotation of the magnet, leading to angular errors in measurement.
Innovation Solution
The use of multiple magnetic field sensors arranged in specific configurations, operating in saturation mode, to suppress stray magnetic fields by combining their output signals and canceling out angular errors, without the need for shielding structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single magnetic field sensor is used to measure angular position, then the device complexity is low, but measurement precision deteriorates due to stray magnetic field interference
Solution Approach 1:
The patent divides the measurement task into multiple independent sensor channels (typically three sensors arranged at different angular positions). Each sensor measures the magnetic field independently, and the results are combined through signal processing to achieve stray field rejection. This segmentation allows the system to distinguish between stray fields (which affect all sensors similarly) and rotation-induced field changes (which vary by sensor position).
Solution Approach 2:
The system uses feedback through signal processing where the outputs of multiple sensors are combined using predetermined coefficients. The processing circuit analyzes the combined signal to extract the true angular position while canceling out stray field components. This feedback mechanism continuously adjusts the measurement to compensate for interference.
2Measurement precision
If shielding structures are added to block stray magnetic fields, then measurement precision improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces mechanical shielding structures with a field-based solution using multiple magnetic field sensors and signal processing. Instead of physically blocking stray fields with magnetic shields or shielding materials, the system uses mathematical cancellation through combined sensor outputs. This substitution eliminates complex manufacturing requirements while achieving the same protection goal.
Solution Approach 2:
The patent introduces signal processing as an intermediary between the magnetic field sensors and the final measurement output. This intermediary layer processes the raw sensor signals to extract the true angular information while filtering out stray field effects. The intermediary enables precise measurement without requiring physical shielding.
3Measurement precision
If multiple magnetic field sensors are used to cancel stray fields, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent merges the outputs of multiple magnetic field sensors through a processing circuit that combines their signals using predetermined coefficients. By merging the sensor outputs in a specific mathematical combination, the system achieves stray field rejection while maintaining a relatively simple overall structure. The merging process integrates multiple measurement channels into a single accurate angular position reading.
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 significantly reduces angular errors by accurately measuring the direction of the magnetic field, enhancing the accuracy, sensitivity, and robustness of angular position measurement systems.
Implementation Method 1
each of the first and second magnetic field sensors being configured to operate in a saturation mode such that the first output signal is indicative of a first direction of the magnetic field at the first magnetic field sensor and the second output signal is indicative of a second direction of the magnetic field at the second magnetic field sensor
Implementation Method 2
Some magnetic field sensors are based upon the magnetoresistive effect in which a material has a tendency to change the value of its electrical resistance in response to an externally-applied magnetic field
Data Source
AI summary
A system for determining angular position includes a magnet having at least four poles and an axis of rotation, wherein the magnet produces a magnetic field. A first magnetic field sensor produces a first output signal and a second magnetic field sensor produces a second output signal in response to the magnetic field. The magnetic field sensors are operated in a saturation mode in which the magnetic field sensors are largely insensitive to the field strength of the magnetic field. Thus, the first output signal is indicative of a first direction of the magnetic field and the second output signal is indicative of a second direction of the magnetic field. Methodology performed by a processing circuit entails combining the first and second output signals to obtain a rotation angle value of the magnet in which angular error from a stray magnetic field is at least partially canceled.