Adaptable Resolution Optical Encoder Using Self-Imaging
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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 providing a range-to-resolution ratio, with prior art failing to offer adaptable configurations that allow multiple encoder resolutions using shared manufacturing techniques and components.
Innovation Solution
The proposed optical displacement encoder configuration includes a scale grating, an illumination source with structured illumination, and a detector system with specific optical components such as lenses and apertures, optimized to produce spatially modulated image light that cooperates with the detector pitch, allowing for high resolution and robust operation with shared components across various resolutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional imaging or self-imaging techniques are used to achieve high resolution, then measurement precision is improved, but device complexity and size increase
Solution Approach 1:
The patent uses self-imaging (Talbot imaging) where the scale pattern creates a virtual copy of itself at a distance, eliminating the need for complex lens systems. The scale grating acts as both the object and the imaging element, with the diffracted light forming a self-image that can be detected directly
Solution Approach 2:
The patent extracts and eliminates unnecessary optical components from conventional imaging systems. By using direct imaging and self-imaging techniques, complex lens assemblies, aperture stops, and intermediate image planes are removed, retaining only the essential scale grating and detector
2Reliability
If telecentric imaging systems are used to improve measurement robustness, then reliability is improved, but device complexity and size increase
Solution Approach 1:
The patent creates a virtual telecentric effect through the self-imaging property where the scale pattern reproduces itself with preserved geometric relationships, eliminating the need for physical telecentric lens systems while maintaining measurement robustness against position variations
Solution Approach 2:
The patent removes complex telecentric lens assemblies and their associated aperture stops, retaining only the essential scale grating and detector arrangement. The self-imaging mechanism inherently provides the robustness previously requiring telecentric optics
3Measurement precision
If high resolution encoders are designed with custom components, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent designs the scale grating to serve multiple functions simultaneously: it acts as the measurement scale, the illumination pattern generator, and the imaging element. This multi-functionality allows a single component to provide various encoder resolutions through different reading points, eliminating the need for multiple custom components
Solution Approach 2:
The patent achieves multiple encoder resolutions by changing the reading position parameter along the scale grating rather than designing different physical components. By reading at different positions (e.g., different Talbot order distances), the same scale grating provides different effective resolutions, reducing manufacturing costs
4Volume of moving object
If compact encoder designs are implemented, then device size is reduced, but measurement range-to-resolution ratio deteriorates
Solution Approach 1:
The patent extends the measurement range by utilizing the longitudinal dimension along the scale grating rather than only the transverse detection dimension. The scale grating can be made very long in one direction while maintaining a compact readhead, allowing large measurement ranges with high resolution through the self-imaging effect at different positions along the scale
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, compact, and cost-effective optical displacement encoders that provide robust operation across different resolutions, utilizing shared manufacturing techniques and components, and is resilient to scale contamination.
Implementation Method 1
The spatially modulated image light comprises fringes formed from the interference of two diffractive orders
Implementation Method 2
an imaging portion positioned to receive operable spatially modulated image light output from the scale grating and output an operable periodic image of the spatially modulated image light
Implementation Method 3
the movement or position of the displaced scale pattern image is detected with a photodetector arrangement
Implementation Method 4
The spatially modulated image light comprises fringes formed from the interference of two diffractive orders
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
A flexible optical displacement encoder configuration uses a source grating (115) to illuminate a scale with structured light such that light from the scale is modulated with a beat frequency envelope which may have a relatively coarse pitch that matches a desired detector pitch. An imaging configuration (180) provides spatial filtering to remove the high spatial frequencies from the modulation envelope to provide a clean signal in the detected fringe pattern. This combination of elements allows an incremental scale track pattern with a relatively finer pitch (e.g., 4, 5, 8 microns) to provide fringes with a coarser pitch (e.g., 20 microns) at a detector. Various scale resolutions can use a corresponding source grating such that all combinations can produce detector fringes that match the same economical detector component.