Hydrophilic DLC Coating for Non-Fogging Optical Encoders
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Solution Overview
Problem
Optical scales and scanning reticles in photoelectric encoders are prone to fogging due to water vapor condensation, leading to reduced optical transmittance and measurement errors, and existing coatings lack adequate scratch and wear resistance.
Innovation Solution
Coating optical scales and scanning reticles with hydrophilic diamond-like carbon (DLC) films, ranging from 30 to 350 nm thick, to enhance mechanical durability and prevent fogging, with optimized thickness and dopants like N, B, Si, or SiOx to achieve a water contact angle below 10°.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If existing protective coatings are applied to optical scales and reticles, then mechanical and chemical protection is improved, but anti-fogging performance deteriorates
Solution Approach 1:
The patent applies a composite coating structure consisting of a hydrophilic bottom layer (such as silicon oxide, silicon oxynitride, or fluorinated compounds) combined with a DLC top layer. This composite structure integrates the anti-fogging properties of the hydrophilic bottom layer with the mechanical durability and scratch resistance of the DLC top layer, simultaneously resolving both protection requirements.
Solution Approach 2:
The patent modifies the surface energy parameters of the coating by incorporating hydrophilic compounds (such as fluorinated compounds, silicon oxide, or silicon oxynitride) that reduce surface tension and increase wettability. This parameter change ensures that condensed water forms a continuous film rather than discrete droplets, preventing optical fogging while maintaining mechanical protection.
2Object-affected harmful factors
If polymeric anti-fogging coatings are used, then anti-fogging performance is improved, but scratch and wear resistance deteriorates
Solution Approach 1:
The patent creates a composite coating where a hydrophilic polymer or inorganic layer (providing anti-fogging properties) serves as the bottom layer, and a DLC layer (providing mechanical strength and scratch resistance) serves as the top layer. This layered composite material approach allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent employs thin film structures where the hydrophilic bottom layer is deposited as a thin conformal coating (typically 1-10 nm) that provides the necessary anti-fogging functionality without adding significant thickness, while the DLC top layer provides the mechanical protection. This thin film approach maintains optical transparency while delivering both required properties.
3Strength
If coating thickness is increased to improve protection, then mechanical durability is improved, but optical transmittance deteriorates
Solution Approach 1:
The patent utilizes ultra-thin film technology where the DLC layer is deposited at controlled thickness (typically 2-20 nm) to provide sufficient mechanical protection and scratch resistance while maintaining optical transparency. The hydrophilic bottom layer is even thinner (1-10 nm), providing anti-fogging functionality with minimal impact on light transmission. This thin film approach achieves the required protection without compromising optical performance.
Solution Approach 2:
The patent optimizes the thickness parameters of each coating layer to achieve the right balance between mechanical protection and optical transmittance. By controlling the DLC layer thickness within specific ranges and using atomic layer deposition or chemical vapor deposition techniques, the coating provides adequate durability while maintaining greater than 90% optical transmittance in the visible spectrum.
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
The hydrophilic DLC films effectively prevent fogging, ensuring high optical transmittance and reducing signal scattering, while improving resolution and specular reflection.
Implementation Method 1
hydrophilic diamond-like carbon (DLC) films... with excellent scratch and wear resistance and anti-fogging properties
Implementation Method 2
Air becomes saturated with water vapor at temperatures below the dew point, and condensation occurs. Water condensation on optically transparent surfaces causes their fogging
Implementation Method 3
The DLC coating may be deposited by various plasma- or ion-based methods
Data Source
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AI summary
The present invention solves the fogging problem of photoelectric linear and rotary encoders used near or below the dew point temperature by coating the complex surface of their optical scales and scanning reticles with hydrophilic diamond-like carbon (DLC) films. These DLC films also increase the scratch and wear resistance of the scales and reticles, thus extending the service life of the encoders. The non-fogging optical scale or scanning reticle contains an optically smooth glass substrate, a lithographically defined micrometer-scale reflective metal pattern on the one glass surface, and a transparent hydrophilic DLC film with a thickness of 30-350 nm grown at least on the one surface. The invention provides a non-fogging optical scale/reticle device and a method capable of easily manufacturing the device.