Optical Encoder Photodetector Array for Contamination Resistance
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Solution Overview
Problem
Existing optical encoders face challenges in maintaining accurate position or displacement measurements due to scale manufacturing defects or contaminants, as current methods either disable the encoder or provide complex signal processing to mitigate errors, which are not effective in all cases.
Innovation Solution
A contamination and defect-resistant optical encoder configuration featuring a photodetector configuration with a set of spatial phase detectors arranged in a specific sequence, where at least a majority of detectors are elongated along the measuring axis and narrow perpendicular to it, allowing for effective cancellation of common mode errors from contaminants and defects without complex signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional photodetector configurations are used, then the encoder can detect position, but contaminants or defects on the scale cause measurement errors
Solution Approach 1:
The photodetector array is segmented into multiple groups (first group, second group, third group) with different orientations. Each group detects signals at different spatial phases, allowing the system to segment the measurement process into multiple independent detection channels that can be processed to eliminate contaminant effects.
Solution Approach 2:
Different photodetector groups are assigned different local qualities - specifically, different orientations (first orientation, second orientation, third orientation) and different spatial phase relationships. This local differentiation in detector properties enables the system to distinguish between true scale features and contaminant artifacts.
2Measurement precision
If complex signal processing is used to mitigate contaminant effects, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The invention extracts the contaminant signal component from the total detected signal by using the specific geometric relationships between photodetector groups. By taking out the common-mode contaminant effect mathematically through signal combination, the system achieves clean measurement signals without requiring complex filtering or processing algorithms.
Solution Approach 2:
The photodetector groups are arranged asymmetrically with respect to the scale pattern - different groups have different orientations and spatial phase relationships. This asymmetric arrangement creates distinct signal characteristics for true displacement versus contaminant effects, enabling simple signal processing to separate and eliminate contaminant contributions.
3Measurement precision
If photodetectors are arranged to detect spatial phases, then displacement measurement is enabled, but susceptibility to scale defects increases
Solution Approach 1:
The invention adds another dimension to the detection system by introducing multiple photodetector groups with different orientations and spatial phases. Instead of relying on a single detection dimension that is vulnerable to defects, the system uses multiple dimensional detection channels that provide redundant and complementary information about the scale pattern.
Solution Approach 2:
The signals from multiple photodetector groups with different orientations and spatial phases are merged through specific signal processing combinations. This merging of multiple detection channels creates a composite measurement that is more robust to individual detector failures or scale defects than any single channel alone.
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 provides accurate displacement signals even with contaminants up to 100 micrometers and defects up to 300 micrometers, ensuring robustness against errors without requiring complex processing, and allows for simple signal processing techniques to determine displacement.
Implementation Method 1
The illumination portion transmits source light to the scale along a source light path. The scale inputs the source light along the source light path and outputs scale light along a scale light path.
Implementation Method 2
Some encoder configurations realize certain advantages by utilizing an illumination source light diffraction grating in an illumination portion of the encoder configuration.
Data Source
AI summary
An optical encoder configuration comprises an illumination portion, a scale, and a photodetector configuration. The illumination portion transmits source light to a scale which outputs a periodic scale light pattern to the photodetector configuration. The photodetector configuration comprises a set of N spatial phase detectors arranged in a spatial phase sequence along a direction transverse to the measuring axis comprising two outer spatial phase detectors at a start and end of the sequence along the direction transverse to the measuring axis. At least a majority of the respective spatial phase detectors are relatively elongated along the measuring axis direction and relatively narrow along the direction perpendicular to the measuring axis direction, and comprise periodic scale light receptor areas positioned corresponding to a respective spatial phase of that spatial phase detector relative to the periodic scale light pattern, and are configured to provide a respective spatial phase detector signal.