Incremental Encoder Reference Mark Signal Distinctness
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Solution Overview
Problem
Fine pitch incremental encoders face challenges in accurately determining the reference position of a readhead relative to a scale, especially when reference marks are small and embedded within incremental features, leading to potential errors due to dirt or fast travel, and existing solutions struggle to provide repeatable reference mark signals.
Innovation Solution
An incremental measurement encoder with a scale and readhead, where the scale features a periodic series of marks and at least one reference mark, utilizing a structured light source and a reference mark photodetector array with unevenly spaced light sources and corresponding photodetector elements, producing a distinct and repeatable reference mark signal by forming a spatially inverted image of the structured light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference mark is embedded within incremental features to provide a positional reference, then the reference position can be determined and accuracy verified, but the reference mark signal becomes difficult to distinguish from incremental signals especially when pitch is less than 20 µm
Solution Approach 1:
The reference mark is segmented into multiple discrete features (first reference mark feature, second reference mark feature, etc.) arranged in a specific pattern. This segmentation allows the reference mark to be distinguished from continuous incremental features while maintaining compact embedding within the fine pitch scale structure.
Solution Approach 2:
The reference mark features are configured with asymmetric spacing or dimensional characteristics that differ from the uniform incremental features. This asymmetry creates a unique optical signature that enables reliable differentiation between reference and incremental signals even at sub-20 µm pitch where features are closely spaced.
2Object-generated harmful factors
If the reference mark is made small to reduce adverse effects on incremental signals, then interference with incremental measurement is reduced, but the reference mark signal becomes weaker and more susceptible to errors from dirt or fast travel
Solution Approach 1:
Different regions of the reference mark are assigned different local qualities - some features are optimized for generating strong optical signals while others are optimized for maintaining compact size. The multi-feature configuration allows certain features to contribute more prominently to signal generation while remaining within the constrained space of fine pitch encoders.
Solution Approach 2:
The reference mark features are pre-configured in specific positions and patterns that anticipate potential detection challenges. The spacing and arrangement are designed beforehand to ensure sufficient optical signal generation even when the reference mark is miniaturized, providing a margin against signal degradation from dirt or rapid motion.
3Device complexity
If a conventional light source is used to illuminate the reference mark, then the system remains simple, but the reference mark signal lacks distinctness and repeatability
Solution Approach 1:
The light source parameters are specifically optimized - using LEDs with particular wavelengths or spectral characteristics that enhance contrast between reference and incremental features. The illumination angle, intensity distribution, and temporal characteristics are tuned to maximize the distinctness of the reference mark signal while maintaining system simplicity.
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 enables accurate and repeatable determination of the readhead's position relative to the reference mark, improving the signal-to-noise ratio and reducing adverse effects on incremental signals, particularly in fine pitch encoders with incremental features less than 20 µm.
Implementation Method 1
the at least one imaging element configured to form a spatially inverted representation of the structured light source so as to form an image of the structured light source onto the reference mark photodetector array
Implementation Method 2
a reference mark photodetector array... producing a distinct and repeatable reference mark signal by forming a spatially inverted image of the structured light source
Data Source
Figure 1(a)~2
Figure 3~4(b)
Figure 5(a)~5(d)
AI summary
An incremental measurement encoder comprising a scale and a readhead. The scale comprises a periodic series of features forming an incremental track and at least one reference mark. The readhead comprising a structured light source and a reference mark photodetector array. The at least one reference mark can comprise at least one imaging element configured to form an image of the structured light source onto the reference mark photodetector array.