Contamination-Resistant Optical Encoder with Dual Illumination Gratings
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Solution Overview
Problem
Existing optical encoders are prone to measurement errors due to scale defects or contamination, and current methods to mitigate these issues often require complex signal processing or simply disable the encoder, lacking effective solutions for continued accurate measurement operations.
Innovation Solution
A contamination and defect-resistant optical encoder configuration featuring a scale grating with narrow, elongated bars and a photodetector configuration with spatial phase detectors arranged in a sequence, which provides displacement signals tolerant to contaminants and defects without complex signal processing, utilizing structured illumination and spatial phase detection to maintain measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical encoder configurations are used, then the encoder can provide displacement measurements, but the measurements are prone to errors due to scale defects or contamination
Solution Approach 1:
The patent divides the illumination function into multiple independent illumination sources (first illumination source and second illumination source), each projecting its own periodic pattern onto the scale. This segmentation allows the system to receive signals from multiple independent channels, so that if one channel is affected by contamination or defects, the other channels can still provide accurate measurement signals.
Solution Approach 2:
The patent changes the parameters of the illumination by using multiple illumination sources with different periodic patterns (different spatial frequencies). Each illumination source creates a distinct fringe pattern with unique characteristics. By varying the spatial frequency parameters of the illumination patterns, the system can maintain measurement accuracy even when certain patterns are degraded by contamination, as other patterns with different parameters remain unaffected.
2Measurement precision
If signal processing methods are used to mitigate contamination effects, then measurement accuracy can be maintained, but the system complexity increases
Solution Approach 1:
The patent employs multiple photodetector arrays (first photodetector array and second photodetector array), each independently detecting the fringe patterns from corresponding illumination sources. The system achieves contamination resistance through the inherent redundancy of having multiple independent detection channels, eliminating the need for complex signal processing algorithms to identify and correct contamination effects. The redundancy itself provides the error mitigation capability.
3Reliability
If multiple illumination sources and photodetector arrays are used, then contamination and defect resistance is improved, but the device complexity increases
Solution Approach 1:
The patent combines multiple illumination sources and multiple photodetector arrays into a single integrated encoder configuration. The first illumination source and first photodetector array work together to provide one measurement channel, while the second illumination source and second photodetector array provide another channel. By merging these components into a unified system with shared mechanical and optical infrastructure, the patent achieves contamination resistance without proportionally increasing overall device complexity.
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 effectively mitigates errors from contaminants and defects, allowing for accurate displacement measurements by canceling common mode errors and compensating for residual errors through spatial phase displacement signals, without the need for complex signal processing, and is tolerant to contaminants up to 100 micrometers and defects up to 300 micrometers.
Implementation Method 1
The structured illumination generating portion comprises a first illumination source diffraction grating and a second illumination source diffraction grating
Data Source
AI summary
An optical encoder configuration comprises a scale, an illumination source, and a photodetector configuration. The illumination source is configured to output structured illumination to the scale. The scale extends along a measuring axis direction and is configured to output scale light that forms a detector fringe pattern comprising periodic high and low intensity bands that extend over a relatively longer dimension along the measuring axis direction and are relatively narrow and periodic along a detected fringe motion direction transverse to the measuring axis direction. The high and low intensity bands move along the detected fringe motion direction transverse to the measuring axis direction as the scale grating displaces along the measuring axis direction. The photodetector configuration is configured to detect a displacement of the high and low intensity bands along the detected fringe motion direction and provide respective spatial phase displacement signals that are indicative of the scale displacement.