Optical Encoder Scale Fine Coarse Pitch Patterns
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Solution Overview
Problem
Conventional optical encoders face issues with position detection accuracy due to unnecessary spatial frequency components in light intensity distributions from scales with multiple modulation pitches, leading to errors in position detection, especially when converting sine waves into position signals.
Innovation Solution
An optical encoder design that incorporates a light source, a scale with both fine and coarse pitch patterns, and a dual detection sensor array system, where high-resolution and low-resolution photodiode arrays detect specific patterns, allowing for the summation of reflectivity or transmittance distributions to eliminate unnecessary frequency components and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a single scale track with multiple modulation pitches is used to obtain a large amount of information, then position detection capability is improved, but unnecessary spatial frequency components are introduced that cause position detection errors
Solution Approach 1:
The patent divides the detection function into separate segments: a first detection sensor array detects the fine pitch pattern while a second detection sensor array detects the coarse pitch pattern. This segmentation prevents the mixing of spatial frequency components that would occur with a single sensor array, thereby eliminating position detection errors while preserving both fine and coarse position information.
Solution Approach 2:
The patent introduces separate detection sensor arrays as intermediaries between the light source and the position detection process. Each sensor array is dedicated to detecting specific spatial frequency components (fine pitch or coarse pitch), acting as a mediator that filters and processes only the relevant information while excluding unnecessary spatial frequency components that would cause errors.
2Loss of information
If multiple modulation pitches are formed on one scale track, then the amount of position information obtained is increased, but the light intensity distribution includes harmful spatial frequency components
Solution Approach 1:
The patent segments the detection process by assigning different sensor arrays to detect different pitch patterns. The first detection sensor array is configured to detect only the fine pitch pattern, while the second detection sensor array detects only the coarse pitch pattern. This segmentation prevents the generation of harmful spatial frequency components that would arise from attempting to detect multiple pitches simultaneously with a single sensor array.
Solution Approach 2:
The patent applies local quality by optimizing each detection sensor array for its specific detection task. The first sensor array has characteristics optimized for detecting fine pitch patterns, while the second sensor array has characteristics optimized for detecting coarse pitch patterns. This localized optimization ensures that each sensor array only picks up the relevant spatial frequency components while filtering out harmful ones.
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 design enables precise position detection by reducing the impact of unwanted spatial frequency components, resulting in accurate relative and absolute position measurements with reduced error, even when power is turned off.
Implementation Method 1
a light source, a scale which is irradiated by the light source and has a fine pitch pattern and a coarse pitch pattern in a measuring direction in one track
Implementation Method 2
a high resolution detection sensor array which receives light from the scale and detects the fine pitch pattern, and a low resolution detection sensor array which receives light from the scale and detects the coarse pitch pattern
Data Source
AI summary
An optical encoder includes a light source, a scale which is irradiated by the light source and has a fine pitch pattern and a coarse pitch pattern in a measuring direction in one track, a high resolution detection sensor array which receives light from the scale and detects the fine pitch pattern, and a low resolution detection sensor array which receives light from the scale and detects the coarse pitch pattern. A transmittance distribution or a reflectivity distribution of the scale is a distribution obtained by summing up a modulation component which corresponds to the fine pitch pattern and in which integrated values in a direction perpendicular to the measuring direction form modulation amplitude uniform in the measuring direction and a modulation component which corresponds to the coarse pitch pattern and in which modulation amplitude is uniform in the measuring direction.