Sloped Cap and Ring Magnet for Accurate Redundant Angle Sensing
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Solution Overview
Problem
Existing magnetic field sensors face challenges in accurately determining the angle of rotation of ferromagnetic objects due to limitations in sensing magnetic fields parallel or perpendicular to the substrate surface, leading to inaccuracies and interference from direct magnetic fields.
Innovation Solution
A redundant sensing system combining inductive and magnetic field sensing elements, utilizing a main coil to induce eddy currents and receive coils with butterfly configurations to detect asymmetric reflected fields, along with magnetic field sensing elements, to determine angular position with enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single magnetic field sensing element (planar Hall or vertical Hall) is used, then the device complexity is low, but the measurement precision of angular position is insufficient due to inability to resolve harmonic errors and interference
Solution Approach 1:
The sensing system is segmented into multiple independent sensing elements (first and second magnetic field sensing elements with different orientations) that each measure specific components of the magnetic field. This segmentation allows the system to resolve harmonic errors by combining measurements from differently oriented elements, improving angular position accuracy without requiring a completely complex alternative sensing system.
Solution Approach 2:
The magnetic field sensing elements serve multiple functions: they detect the fundamental magnetic field for angle determination, and simultaneously provide information for canceling harmonic errors and interference. By processing signals from multiple sensing elements with different orientations, the system achieves both accurate angle measurement and error compensation using the same sensing components.
2Measurement precision
If magnetic field sensing elements are used without harmonic cancellation, then the device complexity is low, but the measurement precision is degraded by harmonic errors and stray field interference
Solution Approach 1:
The system uses feedback by processing signals from multiple magnetic field sensing elements to identify and cancel harmonic errors and interference. The signals from the first and second sensing elements are combined in a specific manner that actively compensates for third-order harmonic errors and stray field interference, improving measurement precision through signal processing feedback mechanisms.
3Measurement precision
If the cap has a flat end, then the manufacturing precision is easy to achieve, but the measurement precision of angular position is reduced due to increased harmonic errors
Solution Approach 1:
The cap's end surface is designed with an asymmetric slant rather than a flat symmetric surface. This asymmetric geometry at the cap end interacts with the magnetic field to reduce third-order harmonic errors in the sensing output. The slanted surface creates a specific magnetic field distribution that improves angular position measurement accuracy while remaining manufacturable.
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 increased angular position accuracy by reducing harmonic errors and interference, allowing for precise angle determination with improved immunity to system variations and stray fields.
Implementation Method 1
a main coil to direct a magnetic field at the target for inducing eddy currents in the target
Implementation Method 2
a receive coil having a butterfly configuration, wherein the receive coil has sine and cosine coils for detecting a reflected field from the target
Implementation Method 3
a magnetic field sensing system to detect the angular position of the target using magnetic field sensing elements
Data Source
AI summary
Methods and apparatus for having heterogenous redundant angle sensing. In embodiments, an angle sensor has inductive sensing and magnetic sensing for a target having a magnetic portion and a metallic portion. In embodiments, the magnetic portion includes a ring magnet centered within the metallic portion, which can be referred to as a cap. In some embodiments, the target-facing side of the cap is sloped. In some embodiments, the target-facing side of the cap and the ring magnet are sloped.