Magnetic Position Measuring Device Harmonic Filtering
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Solution Overview
Problem
Magnetic position measuring devices face inaccuracies due to harmonic distortions in output signals, particularly when filtering higher harmonics and dealing with material inhomogeneities in the scale, which affect the precision of position detection.
Innovation Solution
A magnetic position measuring device with a compact detector system configuration, including multiple detector unit cells and blocks arranged with specific offsets and orientations, generates periodic incremental signals with phase offsets to effectively filter multiple undesired harmonics, such as the third, fifth, seventh, and eleventh harmonics, while minimizing the impact of scale inhomogeneities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional detector configurations are used to filter harmonics, then filtering capability is limited to specific harmonics (e.g., third harmonic), but higher harmonics remain unfiltered affecting measurement precision
Solution Approach 1:
The detector system is segmented into multiple detector unit cells (first, second, third, fourth) with specific geometric arrangements. Each unit cell contains detector elements positioned at calculated distances (e.g., P/12, P/24) to target specific harmonics. This segmentation allows independent optimization of each unit cell for filtering different harmonic orders while maintaining overall system precision.
Solution Approach 2:
The patent employs asymmetric detector element arrangements within unit cells, where detector elements are positioned at non-uniform distances from reference points. For example, in the first detector unit cell, detector elements are arranged with specific asymmetric offsets to create phase differences that selectively cancel third harmonics while preserving fundamental frequency signals.
2Measurement precision
If detector blocks are offset perpendicular to the stripe direction to generate phase-offset incremental signals, then harmonic filtering is achieved, but inhomogeneities in scale material cause amplitude differences reducing detection accuracy
Solution Approach 1:
The patent transitions from perpendicular offsets to offsets primarily along the measuring direction (longitudinal dimension). Detector unit cells are arranged with longitudinal separations (e.g., greater than length L1 in the measuring direction) rather than transverse offsets. This dimensional change maintains the ability to generate phase-offset signals while reducing sensitivity to lateral inhomogeneities in the scale material.
Solution Approach 2:
The invention changes the geometric parameters of detector arrangement, specifically the offset distances and orientations. Instead of fixed perpendicular offsets, the patent uses variable longitudinal offsets combined with specific detector element spacings (P/12, P/24) to achieve phase differentiation. This parameter optimization reduces the impact of material inhomogeneities on signal amplitude consistency.
3Measurement precision
If multiple detector unit cells are arranged with specific offsets to filter multiple harmonics, then comprehensive harmonic suppression is achieved, but the detector system extension increases
Solution Approach 1:
Multiple detector unit cells are merged into a compact detector block structure. The first, second, third, and fourth detector unit cells are integrated with shared components and overlapping measurement zones. This merging allows comprehensive harmonic filtering (third, fifth, seventh, eleventh harmonics) while minimizing the overall longitudinal extension of the detector system along the measuring direction.
Solution Approach 2:
The detector unit cells are arranged in a nested configuration where subsequent unit cells are positioned to overlap with previous ones. For example, the second detector unit cell is offset from the first by distances greater than L1 in the measuring direction, creating a nested arrangement that maximizes filtering coverage within minimized spatial footprint.
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 provides a highly precise filtering of harmonics, ensuring accurate position measurement even with inhomogeneities, by using a compact detector system configuration that effectively suppresses multiple harmonics and reduces the effect of scale inhomogeneities on the filtering process.
Implementation Method 1
Magnetoresistive, thin layers arranged in the form of stripes may be used as detector elements, e.g., Permalloy layers having an anisotropic magnetoresistance. This means that the electrical resistivity in the detector element changes in the presence of an external magnetic field.
Implementation Method 2
Permalloy layers having an anisotropic magnetoresistance. The resistivity change resulting in the detector elements is a function of the external magnetic field, and as the magnetic field strengthens, the characteristic curves of such detector elements experience distortions.
Data Source
AI summary
A magnetic position measuring device includes a magnetic scale and a scanning unit movable relative thereto in at least one measuring direction. The magnetic scale has scale regions positioned at a regular pitch and have an oppositely oriented magnetization, the pitch indicating the extension of a scale region along the measuring direction. The scanning unit has at least one first detector unit cell, which includes three stripe-shaped magnetoresistive detector elements set apart from one another in the measuring direction, the longitudinal directions of the detector elements each having an orientation oriented perpendicular to the measuring direction. Adjacent detector elements along the measuring direction in the first detector unit cell have a distance of, for example, one twelfth of the pitch, relative to one another.