Optical Displacement Measurement Device Stray Light Suppression
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Solution Overview
Problem
The formation of a transparent protective layer on a diffraction grating can lead to stray light interference, causing variations in the interference signal and reducing the accuracy of position detection in optical displacement measurement devices.
Innovation Solution
The thickness of the protective layer is optimized such that the optical path difference between stray light and inherent light is within the range of the coherence curve of the multi-mode semiconductor laser, minimizing interference signal variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transparent protective layer is formed on the diffraction grating surface, then the grating is protected from contamination and grazing, but reflected light is produced on the boundary surface between the protective layer and air, causing stray light interference and reducing position detection accuracy
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness of the protective layer. By carefully selecting and adjusting the thickness parameter, the patent achieves a balance where the protective layer provides adequate protection while minimizing stray light interference. This parameter optimization allows the system to maintain both protection functionality and measurement precision.
2Reliability
If the thickness of the protective layer is increased to improve protection, then more contamination resistance is achieved, but the optical path difference increases causing stronger stray light interference
Solution Approach 1:
The patent employs parameter changes by optimizing the thickness parameter of the protective layer. By finding the optimal thickness value, the patent achieves sufficient protection strength while keeping stray light interference to an acceptable level. This demonstrates how parameter optimization can balance competing requirements.
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 approach improves the interpolation accuracy and detection precision of the optical displacement measurement device by suppressing stray light interference, enhancing the reliability of position detection.
Implementation Method 1
a multi-mode semiconductor laser light source oscillating at a plurality of frequencies, and a diffraction grating moved relative to the multi-mode semiconductor laser light source. The laser light radiated from the multi-mode semiconductor laser light source via the diffraction grating and diffracted by the diffraction grating
Implementation Method 2
reflected light may be produced on a boundary surface between the protective layer and air
Implementation Method 3
The laser light radiated from the multi-mode semiconductor laser light source via the diffraction grating and diffracted by the diffraction grating is made to interfere
Data Source
AI summary
An optical displacement measurement device in which variations in interference light by stray light are suppressed to improve interpolation accuracy and detection accuracy. The surface of diffraction grating 11 is coated with protective layer 12 of thickness L and refractive index n. The protective layer has thickness L such that, with angle θ between a line normal to the protective layer and an incident light beam and an angle θ′ between diffracted light generated by diffraction grating and reflected by boundary surface of protective layer to become stray light to be re-incident on diffraction grating and a line normal to diffraction grating, interference light is of an intensity of interference such that an optical path difference between stray light and light interfering with stray light represented byΔ=2L(n/cos θ′+tan θ′·sin θ)will amount to not higher than 2% of intensity of interference of interference light with optical path length difference Δ=0.