Structured Illumination Optical Encoder Spatial Filtering
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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 that affect measurement accuracy.
Innovation Solution
The proposed optical encoder configuration includes a structured illumination system with a spatial filtering aperture configuration that blocks zero-order light, using a light source, a phase grating, and filtering lenses to produce filtered structured illumination, which is then focused onto a scale grating, ensuring high resolution and compact design while reducing unwanted light errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spatial filtering aperture configuration is used to block zero-order light, then measurement precision is improved, but device complexity increases
Solution Approach 1:
A spatial filtering aperture configuration is introduced as an intermediary component between the illumination portion and the scale grating. This aperture acts as a mediator that selectively blocks zero-order light while allowing first-order light to pass through, thereby improving measurement precision without requiring fundamental redesign of the encoder system
Solution Approach 2:
The harmful zero-order light component is extracted and blocked from the optical path using the spatial filtering aperture configuration. By removing this unwanted light component before it reaches the scale grating, the system achieves improved measurement accuracy while maintaining a relatively simple overall structure
2Measurement precision
If high resolution is achieved through optical encoding, then measurement precision is improved, but device size increases
Solution Approach 1:
The system achieves high resolution by changing optical parameters rather than increasing physical size. Specifically, the resolution is improved by optimizing the illumination fringe pitch, the scale grating pitch, and the spatial filtering characteristics, allowing high measurement precision within a compact encoder volume
3Measurement precision
If residual zero-order light is blocked, then measurement precision is improved, but manufacturing complexity increases
Solution Approach 1:
The spatial filtering aperture configuration is designed as a simple, easily manufacturable component that can be produced using standard optical fabrication techniques. By using a straightforward aperture structure rather than complex optical elements, the system achieves effective zero-order light blocking while maintaining ease of manufacture
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 enhances measurement accuracy by significantly reducing residual zero-order light errors, allowing for higher resolution and compactness while maintaining robustness and cost-effectiveness.
Implementation Method 1
The illumination portion (1560) includes a light source (1530), a phase grating (1550), a first filtering lens (1571), a spatial filtering aperture configuration (1572), and a second filtering lens (1573). The phase grating (1550) diffracts the incident light to produce structured illumination (1531') comprising an illumination fringe pattern (IFP).
Implementation Method 2
the first filtering lens (1571) focuses the structured illumination (1531') to a plane of the spatial filter aperture configuration (1572)
Implementation Method 3
The spatial filtering aperture configuration (1572) includes a central portion (1572c) that blocks zero-order light and an open aperture portion (1572op) that transmits first-order light
Implementation Method 4
the second filtering lens (1573) outputs the structured illumination (1531'') to a plane of the scale grating (1510) as filtered structured illumination with an illumination fringe pitch (PMI)
Data Source
AI summary
An illumination portion is used in an optical encoder which comprises a scale grating, an imaging portion, and a detector portion. A light source outputs light having a wavelength λ. A structured illumination generating portion inputs the light and outputs structured illumination. The structured illumination comprises an illumination fringe pattern oriented transversely to the measuring axis direction. A first filtering lens focuses the structured illumination proximate to a plane of the spatial filter aperture configuration. A spatial filtering aperture configuration includes a central portion that blocks zero-order portions of the structured illumination and an open aperture portion that outputs +1 order and −1 order portions of the structured illumination to a second filtering lens. The second filtering lens outputs the structured illumination to a plane of the scale grating with an illumination fringe pitch PMI along the measuring axis direction at a plane coinciding with the scale grating.