On-Axis Magnetic Angular Position Sensor for Brushless DC Motors
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Solution Overview
Problem
Magnetic angular position sensors in brushless DC motors face challenges due to strong rotating magnets and copper windings that produce time-varying magnetic fields, leading to measurement errors and sensitivity to external disturbances.
Innovation Solution
An on-axis magnetic angular position sensor system with a soft magnetic shaft end portion and a sensor chip containing multiple magnetic field sensor elements, configured to measure magnetic field components in specific directions, combined with a magnetic field source that creates a rotationally symmetric field, allowing for accurate angular position calculation despite disturbing fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic field sensors are used to measure angular position in brushless DC motors, then angular position detection is enabled, but measurement errors occur due to strong rotating magnets and copper windings producing time-varying magnetic fields
Solution Approach 1:
The sensor system segments the magnetic field measurement by using multiple sensor elements arranged in specific patterns (e.g., full-bridge, half-bridge configurations) to measure different components of the magnetic field. This segmentation allows the system to distinguish between the useful magnetic field signal and interfering time-varying fields from motor operation.
Solution Approach 2:
The patent changes the parameters of the magnetic field source by using permanent magnets with specific magnetization patterns (e.g., alternating polarity arrangements) to create a magnetic field with distinct spatial characteristics. This allows the sensor to differentiate between the structured field from the magnet and the unstructured time-varying interference from copper windings.
2Adaptability or versatility
If off-axis magnetic angular position sensors are implemented, then the shaft front side can be inaccessible, but the sensor cannot be mounted on the axis of rotation
Solution Approach 1:
Instead of mounting the sensor off-axis when the shaft front is inaccessible, the patent inverts the approach by using on-axis sensor mounting with the shaft end configured to present a magnetizable surface facing the sensor. This allows the sensor to be positioned on the accessible side while the shaft rotates, effectively solving the accessibility problem.
3Measurement precision
If on-axis magnetic field angle sensors measure magnetic field gradient, then angular position can be determined, but the magnetic field must be measured at two different points arranged symmetrically to the axis of rotation
Solution Approach 1:
The patent merges multiple sensor elements into an integrated sensor chip or module that combines multiple measurement functions. By integrating several magnetic field sensor elements and signal processing circuits into a single unit, the system achieves gradient measurement capability while reducing overall device complexity and simplifying installation.
4Ease of manufacture
If magnetic angular position sensors are designed to be inexpensive, then cost is reduced, but robustness with respect to external magnetic fields and assembly tolerances deteriorates
Solution Approach 1:
The patent converts the harmful effect of external magnetic fields and assembly tolerances into a benefit by using differential measurement techniques. By measuring magnetic field differences between symmetrically arranged sensor elements, the system automatically compensates for external field interference and assembly variations, achieving high robustness without requiring expensive individual sensor components.
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 system provides robust and accurate angular position measurement in brushless DC motors by minimizing the effect of disturbing magnetic fields and assembly tolerances, ensuring reliable operation.
Implementation Method 1
a magnetic field source that magnetizes the shaft end portion, wherein the shaft end portion is formed such that a magnetic field in the sensor plane, which is caused by the magnetic field source, is rotationally symmetric with order N
Implementation Method 2
At least four magnetic field sensor elements are integrated in the sensor chip, wherein two of the magnetic field sensor elements are spaced apart from each other and are only sensitive to magnetic field components in a first direction and wherein two of the magnetic field sensor elements are spaced apart from each other and are only sensitive to magnetic field components in a second direction
Data Source
AI summary
A magnetic angular position sensor system is described herein, which includes a shaft rotatable around a rotation axis, the shaft having a soft magnetic shaft end portion. The system further includes a sensor chip spaced apart from the shaft end portion in an axial direction and defining a sensor plane, which is substantially perpendicular to the rotation axis. At least four magnetic field sensor elements are integrated in the sensor chip, with two of the magnetic field sensor elements being spaced apart from each other and are sensitive to magnetic field components in a first direction and wherein two of the magnetic field sensor elements are spaced apart from each other and are only sensitive to magnetic field components in a second direction, whereby the first and the second direction are mutually non-parallel and the first and the second direction being perpendicular to the rotation axis.