Optical Encoder Dual Lens Spatial Filter High Resolution
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Solution Overview
Problem
Conventional optical displacement encoders fail to provide a combination of high resolution, robustness, large field of view, and cost-effectiveness while maintaining a compact design, which is essential for precision measurement applications.
Innovation Solution
The optical encoder design incorporates a scale grating and a readhead configuration with a moiré grating and detector portion, utilizing a collimated light source, spatial filtering, and a telecentric optical system to produce a primary interference fringe pattern that is detected by multiple detector elements, allowing for high resolution and flexibility in encoder resolutions using shared components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical encoder designs are used, then the encoder can provide basic displacement measurement, but the design cannot simultaneously achieve high resolution, compact size, and cost-effectiveness
Solution Approach 1:
The optical system is segmented into distinct functional components: a first lens for collimation, a second lens for imaging, and a spatial filter with aperture portions. This segmentation allows each component to be optimized independently for its specific function, achieving high resolution through precise control of light paths while maintaining a compact overall design.
Solution Approach 2:
A spatial filter with aperture portions is introduced as an intermediary element between the scale grating and the detector. This spatial filter selectively transmits specific diffracted orders of light while blocking others, enabling high-resolution measurement by isolating the desired spatial frequencies without requiring complex detector arrangements.
2Volume of moving object
If the encoder design is made more compact, then installation convenience is improved, but achieving high resolution and large field of view becomes difficult
Solution Approach 1:
The patent utilizes the spatial frequency domain as an additional dimension for achieving high resolution. By employing a spatial filter that operates in the Fourier domain (selecting specific diffracted orders), the system achieves high measurement precision without requiring proportionally larger physical dimensions, thus maintaining a compact readhead design.
Solution Approach 2:
The system changes the parameter of light propagation from direct imaging to spatial frequency filtering. By transforming the problem from spatial domain imaging to frequency domain filtering through the use of lenses and aperture portions, the encoder achieves high resolution with a compact form factor suitable for various installation environments.
3Adaptability or versatility
If multiple encoder resolutions are required, then measurement versatility is improved, but using shared manufacturing techniques and components becomes more difficult
Solution Approach 1:
The readhead is designed with universal components that can accommodate multiple scale grating pitches. The spatial filter with its aperture portions and the lens configuration can be adjusted or reconfigured to work with different grating periods, allowing a single readhead design to support multiple encoder resolutions through shared manufacturing techniques and components.
Solution Approach 2:
The system incorporates adjustable elements in the optical path, particularly in the spatial filter configuration, that can be dynamically adapted to different scale grating pitches. This dynamic adjustability allows the same hardware platform to provide multiple encoder resolutions by changing the spatial filtering parameters rather than requiring entirely different detector arrangements for each resolution.
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 high-resolution displacement measurement with a compact and cost-effective design, providing a robust and versatile optical encoder suitable for precision applications by using a single detector portion with adaptable moiré grating pitch and spatially modulated fringe patterns.
Implementation Method 1
The scale grating is configured to receive the collimated source light and output diffracted scale light to the first lens
Implementation Method 2
The first lens is configured to receive the scale light and focus it toward the aperture portion
Implementation Method 3
The aperture portion is configured to receive the scale light, block a majority of zero order scale light, and transmit spatially filtered scale light comprising primarily +1 and −1 order scale light toward the second lens
Implementation Method 4
The second lens is configured to receive the spatially filtered scale light and output the spatially filtered scale light toward the moiré grating to form a primary interference fringe pattern
Implementation Method 5
The moiré grating is configured to receive the primary interference fringe pattern and transmit a periodic spatially modulated fringe pattern to the detector portion
Data Source
AI summary
An optical encoder comprises an illumination source, a scale grating extending along a measuring axis direction, an optical portion, a moiré grating, and a detector portion. The optical portion comprises an aperture portion for spatial filtering of scale light from the scale grating. The moiré grating is configured to receive the spatially filtered scale light and output a spatially modulated fringe pattern toward the detector portion. The optical portion outputs the spatially modulated scale light to form a primary interference fringe pattern with a primary fringe pitch PPF. The detector portion comprises at least N respective detector elements positioned to detect N respective spatial phases of the periodic spatially modulated fringe pattern, where N is an integer that is at least three, and each respective detector element has a width dimension DW that is at least as large the primary fringe pitch PPF along a direction of the fringe displacement.