Angled Light Structure in Measurement Encoder Readhead
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Solution Overview
Problem
Existing measurement encoders face significant measurement errors due to adverse structures in the light source, leading to distorted signals and incorrect position determination, particularly in incremental encoders with cyclical errors and absolute encoders with feature misreading.
Innovation Solution
The readhead is configured such that the light structure projected onto the scale is angled, misaligned with respect to the scale's features, effectively reducing measurement errors by splitting the light source into separate point sources and minimizing distortions in the signal output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light source with structure (e.g., LED with current spreaders) is used to illuminate the scale, then the light source can provide sufficient illumination, but the structure in the light projects onto the scale causing measurement errors and signal distortion
Solution Approach 1:
The patent applies asymmetry by deliberately misaligning the structured light source at an angle (e.g., 10-20 degrees) relative to the scale features. This angular offset breaks the symmetry between the light structure and scale markings, preventing the light structure from projecting directly onto the scale features and causing measurement errors. The asymmetric configuration allows the structured light source to maintain illumination while avoiding the formation of distorted interference patterns that would compromise measurement precision.
2Productivity
If the light source structure is aligned with the scale features, then the illumination is optimized, but cyclical errors occur in incremental encoders and feature misreading occurs in absolute encoders
Solution Approach 1:
The patent implements preliminary anti-action by pre-configuring the light source at an angled misalignment before the measurement process begins. This preliminary angular offset prevents the formation of harmful projected structures on the scale that would cause cyclical errors or feature misreading. By establishing this anti-aligning configuration in advance, the system proactively eliminates measurement errors rather than attempting to correct them during operation.
3Measurement precision
If the light source is angled to misalign the structure with scale features, then measurement error is reduced, but the illumination pattern on the scale changes
Solution Approach 1:
The patent applies parameter changes by adjusting the angular parameter of the light source configuration. By changing the angle of the light source from parallel alignment to a misaligned position (e.g., 10-20 degrees offset), the system modifies the illumination pattern parameters to eliminate the projection of light structures onto the scale. This parameter adjustment maintains sufficient illumination intensity while improving measurement precision by preventing distorted interference patterns.
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 significantly reduces cyclical errors and misreading of features, enhancing the accuracy of position determination in both incremental and absolute encoders by minimizing the impact of adverse light structures, resulting in improved measurement precision.
Implementation Method 1
the scale (and often one or more diffraction gratings within the readhead) interacting with light from a source within the readhead to generate at a detector a resultant field (e.g. modulated spot(s) or interference fringes)
Implementation Method 2
the scale (and often one or more diffraction gratings within the readhead) interacting with light from a source
Data Source
AI summary
An encoder apparatus including a scale including a series of features defining at least one scale track and a readhead for reading the scale's features. The readhead includes at least one light source for illuminating the scale and at least one detector. The configuration of the at least one light source is such that there is a structure in the light projected toward the scale. The readhead is configured such that the structure is angled so that it is substantially misaligned with respect to the scale's features so as to reduce measurement error in the signal output by the readhead.