Magnetically encoded scale subfield modulation for low harmonic content
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Solution Overview
Problem
Magnetic position/displacement measuring systems with magnetically encoded scale bodies face challenges in minimizing harmonic content, especially at small air gaps, where the effective field pattern deviates from sinusoidal, leading to high non-linearity and reduced accuracy.
Innovation Solution
The system subdivides main fields into subfields of different types, with varying lengths and encoding strengths, employing periodic or stochastic modulation to minimize harmonics, allowing for high signal-to-noise ratios and low non-linearity even at small air gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor device is positioned at a small distance (small air gap) above the scale body, then the signal strength and signal-to-noise ratio are improved, but the effective field pattern deviates from sinusoidal, causing high harmonic content and non-linearity
Solution Approach 1:
The patent divides each main field into multiple subfields of different types (first type, second type, and third type) with varying lengths and encoding strengths. This segmentation allows the field pattern to be more closely approximated as sinusoidal even at small air gaps, reducing harmonic content while maintaining high signal strength and signal-to-noise ratio
Solution Approach 2:
The patent applies different encoding strengths and field characteristics to different subfields within the encoding track. By varying the length and encoding strength of subfields locally, the system optimizes the field pattern at each position to minimize harmonics while maintaining overall signal quality at small air gaps
2Measurement precision
If the pole widths (length of main fields) are increased, then the signal strength is improved, but the harmonic content increases, making it difficult to compensate with the evaluation device
Solution Approach 1:
The patent segments each main field into multiple subfields with different lengths and encoding strengths. This segmentation allows the system to maintain large overall pole widths for high signal strength while distributing the field across multiple smaller subfields that produce more sinusoidal local patterns, thereby reducing harmonic content
Solution Approach 2:
The patent varies the length and encoding strength parameters of subfields within the encoding track. By changing these parameters locally across different subfields, the system optimizes the balance between signal strength (from large pole widths) and harmonic content (from sinusoidal field patterns)
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 enables accurate position determination with high signal-to-noise ratios and optimized hysteresis, maintaining low non-linearity and high accuracy even at small air gaps, and supports large pole widths by reducing harmonic content.
Implementation Method 1
a magnetically encoded scale body with at least one encoding track and a sensor device with at least one sensor sensitive to the encoding
Data Source
AI summary
A position/displacement measuring system is provided comprising at least one magnetically encoded scale body with at least one encoding track and a sensor device with at least one sensor sensitive to the encoding, the at least one encoding track comprising main fields of at least a first type and a second type which are arranged in a periodically alternating manner in at least a first direction, the subfields of the first type and second type being north pole fields and south pole fields, wherein the main fields of the first type and the main fields of the second type are each subdivided into subfields of at least two different types; wherein a length and/or an encoding strength of the subfields within a main field varies in at least the first direction; and wherein, in the main fields of the first type, the total length in the first direction and/or the total surface of field portions of the first type is greater than the total length and/or the total surface of field portions which are not of the first type, and in the main fields of the second type, the total length in the first direction and/or the total surface of field portions of the second type is greater than the total length and/or the total surface of field portions which are not of the second type.