Optical Encoder Pitch Angle for Contamination Resistance
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Solution Overview
Problem
Existing optical encoders face challenges in maintaining accurate displacement measurements due to scale manufacturing defects or contaminants, as current methods often require complex signal processing or simply disable the encoder, failing to provide continuous accurate 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 specific sequence, which generates and detects a fringe pattern resistant to contaminants and defects, allowing for accurate displacement measurements without complex signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical encoder configurations are used, then the encoder can provide displacement measurements, but manufacturing defects or contaminants on the scale create errors in the measurements
Solution Approach 1:
The patent introduces a pitch angle that tilts the readhead plane relative to the scale plane, creating a three-dimensional geometric relationship. This angular dimension allows the optical path to bypass contaminants on the scale surface while maintaining measurement functionality, effectively using spatial dimensionality to resolve the contradiction between measurement accuracy and contaminant sensitivity
Solution Approach 2:
The patent employs asymmetric positioning of the readhead at a non-zero pitch angle rather than a symmetric zero-angle configuration. This asymmetry creates an optimized optical path that minimizes the impact of contaminants while maintaining measurement precision, resolving the contradiction by breaking the symmetric vulnerability to surface defects
2Measurement precision
If complex signal processing methods are used to mitigate contaminant effects, then measurement accuracy can be maintained, but the device complexity increases
Solution Approach 1:
The patent converts the potentially harmful effect of contaminants into a beneficial geometric filtering mechanism. By using the pitch angle to create an optimized optical path, contaminants that would normally cause measurement errors are naturally excluded from the measurement process, eliminating the need for complex signal processing to remove their effects
3Measurement precision
If the encoder is disabled when contaminants are detected, then measurement errors are prevented, but continuous operation is lost
Solution Approach 1:
The patent implements preliminary anti-action by pre-configuring the optical path with a pitch angle that proactively prevents contaminant interference before it can affect measurements. This preventive geometric design allows the encoder to continue operating accurately despite the presence of contaminants, maintaining both measurement precision and continuous productivity without needing to disable the system
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 configuration effectively mitigates errors from contaminants and defects, enabling continuous accurate displacement measurements by canceling out common mode errors and compensating for residual errors through spatial phase displacement signals, without the need for complex signal processing.
Implementation Method 1
The scale grating is configured to input the illumination fringe pattern at the illumination region and output scale light along a scale light path SCLP that forms a fringe pattern at the photodetector configuration
Implementation Method 2
The photodetector configuration comprises a set of N spatial phase detectors arranged periodically at a detector pitch PD along a detected fringe motion direction transverse to the measuring axis direction
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.