Multi-Wavelength Reflection Inspection for Plastic Container Wall Thickness
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Solution Overview
Problem
Existing optical methods for determining the wall thickness of plastic containers filled with liquid are inadequate, as they rely on light transmission which is affected by the liquid's index of refraction, making it difficult to accurately measure using conventional optical sensing techniques.
Innovation Solution
The method employs multiple wavelengths of light to illuminate the container, with sensors capturing reflections from both inner and outer surfaces, allowing for the computation of wall thickness by comparing absorption characteristics, which is effective even with non-parallel or decorated surfaces and filled containers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical transmission methods are used to measure wall thickness, then the measurement process is simple, but the measurement precision deteriorates when the container is filled with liquid due to refraction effects
Solution Approach 1:
The patent changes the measurement parameter from direct light transmission to light reflection intensity. By measuring the intensity of light reflected from the inner and outer surfaces of the container wall at multiple wavelengths, the system can determine wall thickness without being affected by liquid refraction. The reflection-based measurement parameter is insensitive to the liquid medium inside the container.
Solution Approach 2:
The patent replaces the conventional transmission-based optical measurement system with a reflection-based optical measurement system. This substitution eliminates the harmful refraction effects that occur when light passes through the liquid-filled container, as reflection occurs at the air-plastic interface rather than through the liquid medium.
2Measurement precision
If multiple wavelengths of light are used to illuminate the container, then the ability to determine wall thickness accurately is improved, but the device complexity increases
Solution Approach 1:
The patent employs a single detector that can sense multiple wavelengths of light, making the detector multi-functional. This universal detector replaces what would traditionally require multiple wavelength-specific detectors, thereby reducing device complexity while maintaining the ability to perform accurate wall thickness measurements across different wavelengths.
Solution Approach 2:
The patent combines multiple wavelength detection capabilities into a single detector assembly. By merging the detection function for multiple wavelengths into one device, the system reduces the number of components and simplifies the overall measurement apparatus while preserving the advantages of multi-wavelength illumination.
3Productivity
If off-line sampling inspection is performed, then the equipment complexity is reduced, but the productivity decreases due to periodic inspection intervals
Solution Approach 1:
The patent replaces mechanical cutting and weighing operations with an optical measurement system. This substitution enables continuous, non-contact inspection without the need to stop the production line for sampling, thereby significantly improving productivity while the optical system provides real-time feedback on wall thickness.
Solution Approach 2:
The optical inspection system performs measurements in-line during the normal operation of the blow molder, without requiring separate offline sampling equipment. The system uses the container's own transparency and reflection properties to perform self-measurement, eliminating the need for external sampling apparatus.
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 allows for accurate determination of wall thickness in both filled and unfilled transparent plastic containers, regardless of surface features or liquid content, without requiring positional limiting lenses, providing a non-destructive and efficient inspection process.
Implementation Method 1
a light source for emitting light energy at a portion of the transparent hollow article
Implementation Method 2
light energy at a first, absorption wavelength that is primarily absorbed by the portion of the transparent hollow article
Implementation Method 3
sensing light energy emitted by the light source that is reflected by the portion of the transparent hollow article
Implementation Method 4
a light sensor for sensing light energy emitted by the light source that is reflected by the portion of the transparent hollow article
Data Source
Figure 1~2
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Figure 4
AI summary
An article-inspection apparatus includes a light source for directing light energy with multiple wavelengths at the article and multiple sensors to receive light reflected from external and internal surfaces of the wall of the article, with the reflections being used to compute a physical characteristic, e.g., wall thickness, of the container, due to the light absorption characteristics of the material of the wall of the article. A single light sensitive sensor may be used if the light source wavelengths can be selectively transmitted. The apparatus can be used for inspecting transparent plastic containers that are filled (with a liquid) or unfilled. The apparatus may determine the wall thickness of transparent plastic containers even if they have in-molded features or decorations that make their inner and outer walls non-parallel.