Sickle-Shaped Magnet Arrangement for Rotational Angle Detection
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Solution Overview
Problem
Existing rotational angle detection systems using cylindrical ring magnets and tapered magnets generate impure sine waves due to their magnetic field measurements, leading to inaccuracies in rotational angle detection, with errors often exceeding 1° due to high harmonic content and anomalies in the sine wave.
Innovation Solution
A sickle-shaped magnet arrangement is employed, where the first sickle-shaped portion is magnetized in one direction and the second sickle-shaped portion in a different direction, forming a magnetic field that produces a relatively pure sine wave when measured by magnetic sensors, allowing for accurate rotational angle detection within 1° by varying radial thickness and axial thickness based on azimuthal coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cylindrical ring magnets or tapered magnets are used for rotational angle detection, then the device structure is simple and easy to manufacture, but the measurement precision deteriorates due to impure sine waves and high harmonic content causing errors exceeding 1°
Solution Approach 1:
The magnet arrangement is segmented into multiple sickle-shaped portions (first sickle-shaped portion, second sickle-shaped portion, etc.) arranged circumferentially around the rotational axis. Each portion is magnetized in a specific direction to generate magnetic field components that combine to form a pure sine wave, thereby improving measurement precision while maintaining manageable structural complexity through modular segmentation
Solution Approach 2:
The sickle-shaped magnet portions feature asymmetric geometry with varying radial widths across different azimuthal coordinates. This asymmetric shape is specifically designed to generate the required magnetic field distribution that produces a pure sine wave, resolving the contradiction by using controlled geometric asymmetry to achieve high measurement accuracy without excessive complexity
2Measurement precision
If the inner radius or outer radius of the magnet arrangement varies based on azimuthal coordinate to improve sine wave purity, then the measurement precision improves, but the manufacturing precision requirements increase
Solution Approach 1:
The sickle-shaped magnet portions exhibit local quality variations where the radial width changes at different azimuthal coordinates around the rotational axis. This local variation in geometry is deliberately designed to optimize the magnetic field distribution and sine wave purity at specific locations, achieving high measurement precision while the localized nature of the variations makes manufacturing more feasible compared to global complexity
3Measurement precision
If multiple sickle-shaped portions with different magnetization directions are used to generate pure sine wave, then the measurement precision improves within 1° accuracy, but the device complexity increases
Solution Approach 1:
Multiple sickle-shaped magnet portions with different magnetization directions are merged into a single integrated magnet arrangement that rotates together around the rotational axis. This merging approach combines the magnetic field contributions of individual portions to generate a pure sine wave, achieving high measurement precision (within 1° accuracy) while presenting a unified structure that manages 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 sickle-shaped magnet arrangement significantly reduces harmonic content in the magnetic field, enabling precise rotational angle measurement by generating a pure sine wave, thus improving detection accuracy to within 1° and enhancing the robustness of the rotational angle detection system.
Implementation Method 1
an inner circumferential surface and an outer circumferential surface form a first sickle-shaped portion and a second sickle-shaped portion, wherein the first sickle-shaped portion is magnetized in a first direction and the second sickle-shaped portion is magnetized in a second direction
Data Source
AI summary
An example includes a sickle-shaped magnet arrangement, for use in determining a rotational angle of a rotatable object and is configured to co-rotate with the rotatable object around a rotational axis, includes an inner circumferential surface having an inner radius that is based on an azimuthal coordinate of the sickle-shaped magnet arrangement, an outer circumferential surface having an outer radius that is based on the azimuthal coordinate of the sickle-shaped magnet arrangement, wherein at least the inner radius or the outer radius varies based on the azimuthal coordinate; and an axial thickness between a first end of the sickle-shaped magnet arrangement and a second end of the sickle-shaped magnet arrangement, wherein the inner circumferential surface and the outer circumferential surface form a first sickle-shaped portion and a second sickle-shaped portion, wherein the first sickle-shaped portion is diametrically opposite the second sickle-shaped portion, and wherein the first sickle-shaped portion is magnetized in a first direction and the second sickle-shaped portion is magnetized in a second direction that is within a threshold angle of the first direction and different from the first direction.