Absolute Encoder Magnetic Shielding for Flux Interference
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Solution Overview
Problem
In absolute encoders that detect the rotation of multiple permanent magnets, the accuracy of the magnetic rotation angle sensor can be compromised by unintended magnetic flux from the permanent magnets, necessitating a structure to mitigate this interference.
Innovation Solution
The absolute encoder incorporates a magnet with adjacent N-pole and S-pole formations in both radial and axial directions, and a magnetic interference reduction member made of magnetic material on its outer peripheral surface, to reduce the influence of unintended magnetic flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple permanent magnets are provided to detect rotation over multiple rotations, then the ability to identify absolute position over multiple rotations is improved, but unintended magnetic flux from the permanent magnets interferes with the magnetic rotation angle sensor causing decreased detection accuracy
Solution Approach 1:
A magnetic shielding member is introduced as an intermediary component between the permanent magnets and the magnetic rotation angle sensor. This shielding member selectively blocks unintended magnetic flux paths while allowing the necessary magnetic flux for rotation detection to pass through, thereby mediating the interaction between the magnets and sensor to eliminate interference
Solution Approach 2:
The magnetic shielding member is positioned specifically at locations where unintended magnetic flux interferes with the sensor, providing localized magnetic shielding only where needed. This allows the permanent magnets to maintain their full functionality for detecting rotation angle while protecting the sensor from harmful magnetic interference in specific regions
Data Source
AI summary
To reduce the influence of an unintended magnetic flux of a permanent magnet on detection accuracy. An absolute encoder (2) includes a magnet provided at a tip end side of any one of a first worm gear portion (11) and a second worm gear portion (22), and an angle sensor configured to detect a rotation angle of the magnet in response to a change in magnetic flux generated from the magnet. In the magnet, a first magnetic pole portion of a first polarity and a second magnetic pole portion of a second polarity different from the first polarity are formed adjacent to each other as viewed from an axial end surface of the magnet. The first magnetic pole portion and the second magnetic pole portion are formed adjacent to each other in a radial direction with a radial center of the magnet as a boundary, and the first magnetic pole portion and the second magnetic pole portion are formed adjacent to each other in an axial direction with an axial center as a boundary. The absolute encoder (2) is provided with a magnetic interference reduction member formed of a magnetic material on a radially outer peripheral surface of the magnet.