Structured Illumination Spatial Filter Optical Encoder
Find Innovative SolutionsGenerate Solutions
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-generating portion with a spatial filtering aperture configuration that blocks zero-order light, using a light source, a first and second filtering lens, and a spatial filtering aperture to ensure only +1 and -1 order light reaches the scale grating, enhancing measurement accuracy and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase grating or blocking portion is used to block zero-order light, then measurement accuracy is improved, but residual zero-order light errors still affect the signal
Solution Approach 1:
The patent extracts and removes the harmful zero-order light component from the optical path using a spatial filter positioned at the Fourier plane. The spatial filter selectively blocks the zero-order diffraction light while allowing the first-order diffracted light to pass through to the scale grating, thereby eliminating the source of measurement errors caused by residual zero-order light interference.
Solution Approach 2:
The patent introduces a spatial filter as an intermediary element in the optical path between the light source and the scale grating. This spatial filter acts as a mediator that selectively transmits desired first-order diffracted light while blocking harmful zero-order light, thereby improving measurement accuracy without directly modifying the scale grating or detector.
2Measurement precision
If high resolution is achieved through detailed optical arrangements, then measurement precision is improved, but device size increases
Solution Approach 1:
The patent employs a doubly telecentric imaging system that serves multiple functions simultaneously: it provides high-resolution imaging of the scale grating, maintains a constant magnification factor across the field of view, and enables compact encoder design. The telecentric arrangement allows the same optical system to achieve both high measurement precision and compact dimensions by optimizing the optical path and component placement.
Solution Approach 2:
The patent optimizes key optical parameters including the focal lengths of imaging lenses, the pitch of the scale grating, and the distance between optical components to achieve high resolution in a compact form factor. By carefully selecting and adjusting these parameters, the system attains fine measurement resolution without requiring a large physical volume.
3Ease of manufacture
If multiple encoder resolutions are provided using shared components, then cost is reduced, but design complexity increases
Solution Approach 1:
The patent designs the optical system with universal components that can support multiple encoder resolutions. The doubly telecentric imaging system and spatial filter configuration are designed to work with scale gratings of different pitches, allowing a single optical platform to provide multiple resolution levels (e.g., 0.5 micrometer and 2 micrometer resolutions) without requiring separate dedicated optical systems for each resolution.
Solution Approach 2:
The patent enables dynamic selection of different encoder resolutions by allowing the system to adapt to different scale grating pitches. The optical system maintains its performance characteristics across different configurations, enabling flexible resolution selection based on application requirements while using the same fundamental optical components.
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 residual zero-order light errors, improving the encoder's resolution, range-to-resolution ratio, and compactness, allowing for multiple resolutions using shared components and manufacturing techniques, thereby enhancing measurement precision and cost-effectiveness.
Implementation Method 1
a phase grating in an illumination portion to substantially block zero-order light from reaching an encoder scale grating
Implementation Method 2
WO2008/030681A2 discloses an interferometric optical position encoder employing spatial filtering of diffraction orders other than +/- 1st diffraction orders
Implementation Method 3
The first filtering lens focuses the structured illumination to a plane at the spatial filter aperture configuration
Implementation Method 4
the second filtering lens transmits the spatially filtered structured illumination to a plane of the scale grating as filtered structured illumination with an illumination fringe pitch
Implementation Method 5
U.S. Patent Nos. 7,186,969; 7,307,789; and 7,435,945 disclose various encoder configurations that utilize either singly or doubly telecentric imaging systems for imaging the periodic pattern of light and sensing displacement of the periodic scale structure
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
An illumination portion is used in an optical encoder which comprises a scale grating (110), an imaging portion (180), and a detector portion (120). A light source outputs light having a wavelength ». 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 P MI along the measuring axis direction at a plane coinciding with the scale grating.