Structured Illumination Optical Encoder for Precision Displacement
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Solution Overview
Problem
Existing optical displacement encoders face challenges in achieving a combination of high resolution, compact size, robustness, and cost-effectiveness while minimizing residual zero-order light errors, which affect the accuracy of displacement measurements.
Innovation Solution
The proposed optical displacement encoder configuration incorporates a structured illumination system with a beam separating portion and an illumination grating that diffracts only two orders of light across the scale track, ensuring that only the desired diffracted light is imaged to the detector, thereby reducing residual zero-order light errors and enhancing measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a telecentric imaging system is used to image the scale pattern, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The optical system is divided into separate functional modules: a first telecentric lens for imaging the scale pattern, a second telecentric lens for imaging the readout pattern, and a beam splitter to combine the beams. This segmentation allows each lens to be optimized for its specific function while maintaining overall system precision without requiring a single complex lens design.
Solution Approach 2:
A beam splitter is introduced as an intermediary element between the two telecentric lenses. The beam splitter combines the beam from the first lens (containing scale pattern information) with the beam from the second lens (containing readout pattern information), enabling both patterns to be imaged simultaneously on the photodetector array without requiring a single complex optical path.
2Ease of operation
If the readhead and scale are made compact, then ease of installation is improved, but manufacturing precision becomes more difficult to achieve
Solution Approach 1:
The patent replaces mechanical precision requirements with optical principles. By using telecentric lenses that inherently provide uniform magnification and eliminate perspective errors, the system achieves high manufacturing precision without requiring extremely tight mechanical tolerances on the compact readhead and scale components.
Solution Approach 2:
The optical parameters of the telecentric lenses are carefully selected and optimized to achieve the desired encoder resolution within a compact form factor. By adjusting lens focal lengths, diameters, and spacing, the system achieves high precision measurements without requiring large physical dimensions, thus resolving the contradiction between compact size and manufacturing precision.
3Device complexity
If multiple encoder resolutions are provided using shared components, then device complexity is reduced, but measurement precision may be compromised
Solution Approach 1:
The telecentric lens system is designed to be multi-functional, capable of supporting multiple encoder resolutions by varying the pitch of the scale pattern and readout pattern. The same basic optical components (two telecentric lenses and beam splitter) can be used across different resolution configurations, reducing device complexity while maintaining precision through software or pattern design rather than hardware changes.
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 improves the resolution-to-range ratio, achieves a compact design, and reduces manufacturing complexity, allowing for multiple encoder resolutions using shared components, while minimizing errors and enhancing measurement precision.
Implementation Method 1
an illumination grating configured to diffract the source light across an operating gap to the scale track
Implementation Method 2
a beam separating portion configured to output a first source light portion and a second source light portion to the illumination grating, such that the first source light portion and the second source light portion form beams that are spaced apart from one another
Implementation Method 3
The scale track is configured to spatially modulate the input illumination fringe pattern and output scale light comprising spatially modulated image light
Implementation Method 4
an imaging portion configured to image only scale light arising from an imaged region of the scale track to the detector configuration
Data Source
AI summary
An illumination portion of an optical encoder comprising a scale track extending along a measuring axis direction, an imaging portion, and a detector configuration. The illumination portion comprises: a light source configured to output source light; a collimation portion; and a structured illumination generating portion comprising a beam-separating portion and an illumination grating and configured to input the source light and output structured illumination to the scale track. The beam-separating portion is arranged to input the source light and output a first source light portion and a second source light portion to the illumination grating, such that they form beams that are spaced apart from one another along the measuring axis direction. The illumination grating is configured to diffract the first and second source light portions to the scale track such that only two orders of diffracted light overlap within an imaged region.