Magnetic Encoder With Varying Pole Shapes To Cancel Interference
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Solution Overview
Problem
In small format magnetic encoders, the close proximity and small size of tracks lead to significant magnetic field interference between adjacent tracks, causing harmonic distortion in sensor outputs due to manufacturing tolerances and differing numbers of magnets, which complicates secure fixing and accurate position measurement.
Innovation Solution
The design incorporates varying pole shapes and sizes along one track to create keying portions that provide mechanical fixing while also canceling out periodic magnetic field variations from adjacent tracks, using cut-away edges or shapes to reduce field strength where interference is greatest, and employing a backing member with an adhesive and mechanical fixing mechanism to secure the encoder element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small magnetic encoder regions are used and packed close together to meet packaging constraints, then the encoder can accommodate severe packaging constraints, but magnetic field interference between adjacent tracks increases causing harmonic distortion
Solution Approach 1:
The encoder element features poles with varying shapes and sizes at different locations along the track. Specifically, certain poles have cut-away edges or reduced dimensions in regions where magnetic field interference from adjacent tracks is most severe. This local modification of pole geometry creates position-dependent field strength variations that cancel out the harmful interference patterns, allowing small encoder size while maintaining measurement accuracy.
2Measurement precision
If two parallel tracks with different numbers of poles are used to provide high resolution and low resolution measurements, then measurement resolution is improved, but magnetic field interference between tracks increases
Solution Approach 1:
The encoder element features poles with varying shapes and sizes at different locations along the track. Specifically, certain poles have cut-away edges or reduced dimensions in regions where magnetic field interference from adjacent tracks is most severe. This local modification of pole geometry creates position-dependent field strength variations that cancel out the harmful interference patterns, allowing small encoder size while maintaining measurement accuracy.
3Ease of manufacture
If manufacturing tolerances vary causing sensor location variations, then manufacturing flexibility is maintained, but harmonic distortion of sensor outputs increases
Solution Approach 1:
The varying pole shapes are deliberately designed to counteract the harmful effects of manufacturing tolerances and sensor location variations. By creating controlled, known variations in pole geometry, the system converts potential sources of error (tolerance variations) into a compensating mechanism that actively reduces harmonic distortion. The asymmetric pole configurations create field patterns that cancel out the unpredictable variations caused by manufacturing tolerances.
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
This approach effectively reduces harmonic noise and ensures secure fixing of the encoder, maintaining high resolution and accuracy in position measurement while accommodating packaging constraints, by minimizing the impact of inter-track magnetic field interference.
Implementation Method 1
The magnetic poles can be formed by locally magnetising regions of a material which can be permanently magnetized
Implementation Method 2
varying pole shapes and sizes along one track to create keying portions that provide mechanical fixing while also canceling out periodic magnetic field variations from adjacent tracks
Data Source
AI summary
A magnetic encoder comprising an encoder element having at least two tracks of encoder regions, each region comprising a magnetic pole, the poles along each track being arranged as an alternating pattern of North and South poles, and one or more sensors, each sensor comprising one or more sensing elements associated with a respective track and generating an output that is indicative of the magnetic field associated with that track in the vicinity of the sensor, in which at least one track has a differing number of poles to at least one of the other tracks, and in which the properties of the poles of a first one of the tracks differ along the track such that there is a periodic variation along the first track of the magnetic field emitted by the first track that is detected by the sensing elements associated with the first track which at least partially cancels out a corresponding periodic variation in field from the other tracks that is also detected by the sensing elements associated with the first track.