Magnetic Encoder Period Assessment via Discrete Fourier Transform
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Solution Overview
Problem
Existing magnetic encoder systems require precise matching of the pitch of the magnetic scale to the magnetic sensor elements, which is impractical and limits their application, especially in rotary encoders with radially extending magnetic segments where tight mounting tolerances are needed.
Innovation Solution
A magnetic encoder apparatus that uses a periodically repeating magnetic pattern with alternating magnetized regions, allowing the analyser to assess the period of the pattern using discrete Fourier transformation, eliminating the need for an integer number of sensor elements per scale period and enabling flexible alignment and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pitch of the magnetic scale is precisely matched to the pitch of the magnetic sensor elements, then measurement precision is improved, but device complexity and manufacturing difficulty increase due to tight mounting tolerances
Solution Approach 1:
The patent changes the fundamental parameter of pitch matching by allowing the magnetic scale pitch to differ from the sensor element pitch. Instead of requiring precise matching, the system uses a plurality of sensor elements (at least four) spaced at intervals that do not necessarily correspond to integer divisions of the scale pitch. The analyser compensates for this mismatch by calculating position based on the combined signals from multiple sensors, thereby resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If an integer number of sensor elements per scale period is required, then measurement precision is improved, but ease of manufacture deteriorates due to strict alignment requirements
Solution Approach 1:
The patent divides the measurement function across multiple sensor elements rather than relying on a single sensor per scale period. By using at least four sensor elements spaced at non-integer intervals relative to the scale pitch, the system segments the measurement task so that individual element misalignments are compensated by the collective signal processing in the analyser, thereby improving ease of manufacture while maintaining precision.
Solution Approach 2:
The analyser performs multiple functions: it processes signals from multiple sensors, determines the actual pitch of the magnetic scale, compensates for misalignment, and calculates position. This multi-functionality allows the system to achieve accurate measurements without requiring strict alignment or integer relationships between sensor pitch and scale pitch, thereby improving ease of manufacture.
3Measurement precision
If tight mounting tolerances are enforced for pitch matching, then measurement precision is improved, but ease of operation deteriorates due to difficult installation and adjustment
Solution Approach 1:
The patent introduces dynamic adaptation in the analyser that automatically adjusts to the actual pitch relationship between the magnetic scale and sensor elements. Rather than requiring static precision in mounting, the system dynamically determines the pitch ratio and compensates for misalignment during operation. This makes installation easier while maintaining measurement precision through real-time adaptation.
4Adaptability or versatility
If the pitch of magnetic sensor elements differs from the pitch of the magnetic pattern, then adaptability is improved, but device complexity increases due to need for pitch assessment and correction algorithms
Solution Approach 1:
The analyser performs self-calibration by automatically determining the actual pitch of the magnetic scale from the signals received from the sensor elements. The system serves itself by detecting the pitch relationship and adjusting its calculations accordingly, without requiring external calibration or complex manual configuration. This self-service approach enables adaptability while keeping the added complexity manageable and automatic.
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 solution allows for accurate position measurement without requiring precise pitch matching, enhancing the flexibility and accuracy of magnetic encoder systems, particularly in rotary encoders, by assessing the period of the magnetic pattern and adjusting for misalignment.
Implementation Method 1
a magnetic scale that produces a periodically repeating magnetic pattern, a plurality of magnetic sensor elements for reading the magnetic scale
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
Magnetic encoder apparatus (2) is described that comprises a plurality of magnetic sensor elements (e.g. Hall sensors) for reading an associated magnetic scale (4; 10) that produces a periodically repeating magnetic pattern. The plurality of magnetic sensor elements produce a plurality of sensor signals and an analyser (7) is provided for analysing the plurality of sensor signals to provide a measure of the position of the magnetic sensor elements relative to the associated magnetic scale (4; 10). The analyser (7) is arranged to use the plurality of sensor signals to assess the period (60) of the periodically repeating magnetic pattern sensed by the plurality of magnetic sensor elements. In this manner, the requirement to carefully match the period of the sensor elements with the periodically repeating magnetic pattern of the associated magnetic scale (4; 10) is avoided.