Weighted Detector Array Encoder for Phase-Accurate Position Sensing
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Solution Overview
Problem
Existing encoders face challenges in precisely detecting the position of a scale due to phase accuracy issues caused by mounting height offsets and image magnification errors between the light source and the light receiving element, leading to reduced detection precision.
Innovation Solution
An encoder design that includes a scale with spatially modulated patterns, a detector array, and a signal processor with a weighting unit to weight output signals from detectors based on their position, ensuring that the spatial frequency corresponding to the second modulation period is equal to or smaller than the non-weighted value, thereby reducing errors and improving detection precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single modulation period is used in the incremental pattern, then the structure is simple and easy to manufacture, but the detection precision is limited due to mounting height offsets and image magnification errors
Solution Approach 1:
The incremental pattern is segmented into multiple modulation periods (first modulation period and second modulation period) with different spatial frequencies. This segmentation allows the system to process different frequency components separately, enabling high-precision position detection while compensating for mounting errors through the combined information from multiple periods
Solution Approach 2:
Different regions of the pattern row are assigned different modulation periods and spatial frequencies. The first modulation period provides coarse position information while the second modulation period provides fine position information. This local differentiation of pattern properties enables the system to achieve high detection precision without requiring uniform complexity throughout the entire pattern structure
2Measurement precision
If multiple modulation periods are used to improve precision, then position detection accuracy improves, but the device complexity increases
Solution Approach 1:
The pattern employs periodic modulations with different periods (first and second modulation periods) encoded in the spatial domain. By using periodic patterns with known frequencies, the signal processor can apply frequency-domain analysis techniques to extract position information from each period separately, managing the complexity through systematic periodic structure rather than arbitrary complex patterns
Solution Approach 2:
The system changes the spatial frequency parameter across different regions of the pattern row. The first modulation period uses one spatial frequency while the second modulation period uses a different spatial frequency. This parameter variation allows the signal processor to distinguish between different frequency components and extract position information with high precision, while the regular parametric changes keep the overall structure manageable
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 proposed solution enhances the precision of relative and absolute position detection by minimizing the impact of spatial frequency fluctuations and magnification errors, resulting in improved detection accuracy and design flexibility.
Implementation Method 1
a pattern row that has a plurality of patterns configured to spatially modulate an energy distribution
Implementation Method 2
a detector array that includes a plurality of detectors that are configured to detect the energy distribution from the pattern row
Data Source
AI summary
An encoder includes a scale, a detector array that includes a plurality of detectors, and a signal processor configured to process and convert into positional information, an output signal from the detector array. The signal processor includes a first phase acquirer configured to acquire a first phase of a first modulation period from an output signal of the detector array. The encoder further includes a weighting unit configured to weight an output signal from each of a plurality of detectors using a weight in accordance with a position of the detector array. The weight is set so that in a predetermined range that contains a spatial frequency corresponding to the second modulation period in a spatial frequency response of the first phase acquirer, a value weighted by the weighting unit is equal to or smaller than a non-weighted value.