Rotary Magnetic Encoder Angle Error Reduction
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Solution Overview
Problem
Rotary magnetic encoders face issues with shaft misalignment leading to signal noise, positional errors, and 'Quiver' due to non-uniform magnetic field distribution and angular velocity variations, especially at high speeds.
Innovation Solution
A shaft misalignment tolerant rotary magnetic encoder design employing a friction reducer and magnetic anchor to minimize contact and friction between the sensor magnet and the drive magnet, using a spherical bearing or thrust bearing arrangement to maintain precise alignment and reduce dynamic friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the internal magnet is allowed to rotate freely within the encoder housing, then the encoder can operate without shaft bearings, but the magnet may come into contact with the housing causing non-uniform angular velocity and angle error
Solution Approach 1:
A friction reducer (bearing) is introduced as an intermediary component between the internal magnet and the encoder housing. This bearing supports the magnet during rotation, preventing contact with the housing while maintaining rotational freedom, thereby eliminating angle error caused by non-uniform angular velocity
Solution Approach 2:
The patent replaces the traditional shaft bearing system with a magnet bearing arrangement where the friction reducer is directly coupled to the internal magnet. This substitution eliminates the need for external shaft bearings while maintaining precise rotational support and alignment
2Productivity
If the internal magnet rotates at high speeds, then productivity increases, but the magnet may levitate or float causing drag and angle error
Solution Approach 1:
The friction reducer serves as a mediator that maintains continuous contact with the internal magnet during high-speed rotation. This prevents the magnet from levitating or floating, eliminating drag forces that would cause angle error while allowing high rotational speeds for improved productivity
Solution Approach 2:
The friction reducer provides beforehand support to the internal magnet, preventing levitation before it can occur during high-speed operation. This prior cushioning ensures stable rotational motion and consistent angular velocity throughout the operating range
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 effectively minimizes angle error and 'Quiver' by ensuring uniform magnetic field distribution and stable angular velocity, even at high rotational speeds, without the need for external shaft bearings, resulting in improved tracking accuracy and reduced drag.
Implementation Method 1
rotation of the encoder shaft rotates the external drive magnet substantially in unison therewith magnetically coupling the external magnet to the internal magnet within the encoder housing causing the internal magnet to rotate substantially in unison with the external drive magnet
Implementation Method 2
The friction reducer is a bearing arrangement that provides a reduced contact surface area with the sensor magnet preventing stiction and reducing variations in sensor magnet angular velocity
Implementation Method 3
Magnetic coupling is enhanced and can be increased by a magnetic anchor disposed between the sensor magnet and the drive magnet that pulls the rotating sensor magnet towards the drive magnet maintaining friction reducing contact between the sensor magnet and the friction reducer
Data Source
AI summary
A rotary magnetic encoder assembly of noncontact or “contactless” construction having an internally disposed first exciter or sensor magnet magnetically coupled to an externally disposed second application or drive magnet attached to an encoder shaft that rotates the sensor magnet substantially in unison therewith during encoder shaft rotation. The sensor magnet is rotatively supported by a friction reducer that is a bearing arrangement that provides point bearing contact preventing stiction and reducing dynamic friction of the sensor magnet minimizing angle error and helping to prevent “Quiver.” In one embodiment, the friction reducer is a spherical ball bearing. In another embodiment, the friction reducer is a thrust bearing that includes a spindle carrying the sensor magnet. A magnetic anchor can be disposed between the sensor magnet and drive magnet to help keep the sensor magnet in point bearing contact during rotation further minimizing angle error.