Rotary Encoder Shielded Magnet Design
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Solution Overview
Problem
Rotary encoders using magnetic field sensors face accuracy issues due to distortion from external magnetic fields, particularly in angular ranges exceeding 180 degrees, where the magnetic field generated by permanent magnets can be disrupted.
Innovation Solution
A magnetic setup comprising a rotatable permanent magnet with a through-hole extending along the rotation axis, surrounded by a soft magnetic sleeve for shielding against external fields, and a magnetic field sensor placed within the through-hole to minimize distortion effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a permanent magnet is used for generating the magnetic field in the rotary encoder, then the encoder can detect angular position and velocity, but the magnetic field is distorted by external magnetic fields leading to reduced measurement accuracy
Solution Approach 1:
A soft magnetic shield is introduced as an intermediary component between the permanent magnet and external magnetic fields. The shield comprises a first soft magnetic layer and a second soft magnetic layer with different magnetic permeabilities, creating a layered protective barrier that selectively interacts with external magnetic fields while preserving the encoder's measurement function.
Solution Approach 2:
The magnetic shield is constructed using composite material structure with two distinct soft magnetic layers having different magnetic permeabilities. This composite approach allows optimization of shielding effectiveness across different frequency ranges and field strengths, combining the advantages of materials with high permeability (for low-frequency shielding) and moderate permeability (for high-frequency shielding).
2Measurement precision
If a soft magnetic shield is added to protect against external magnetic fields, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The shield design optimizes the magnetic permeability parameter by using two layers with different permeability values. This parameter-based differentiation allows each layer to target specific frequency ranges of external magnetic fields, achieving comprehensive shielding with relatively simple layer structures rather than requiring complex geometric configurations.
Solution Approach 2:
The shield is segmented into two distinct layers with different magnetic properties, allowing each layer to perform a specialized function in the shielding process. This segmentation enables the system to handle different types of magnetic interference (low-frequency vs. high-frequency) through dedicated layers, simplifying the overall design compared to using a single complex shield structure.
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 solution significantly reduces the sensitivity of rotary encoders to external magnetic fields, enhancing measurement accuracy and reliability across various angular positions and velocities.
Implementation Method 1
a soft magnetic sleeve encompassing the rotation axis and thus the permanent magnet arrangement for shielding against external magnetic fields
Implementation Method 2
The magnetization is usually perpendicular to the rotation axis thus giving rise to a magnetic field, which is thus predominantly perpendicular to this axis
Implementation Method 3
A magnetic field sensor is placed in front of the magnet. If the axis rotates the magnetic field also rotates and the rotation can be detected by the magnetic field sensor
Data Source
AI summary
A magnetic set-up for use in a rotary encoder is disclosed. The set-up includes a permanent magnet arrangement including at least one permanent magnet, which is rotatable with respect to a rotation axis, and a soft magnetic sleeve encompassing the rotation axis and thus the permanent magnet arrangement for shielding against external magnetic fields. The at least one permanent magnet includes a through-hole, which extends along the rotation axis, so that the permanent magnet fully extends around the rotation axis.