Diffraction Thickness Measurement Using Aperture Light Filtering
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Solution Overview
Problem
Existing thickness measurement techniques in manufacturing environments face challenges in achieving high accuracy and robustness due to noise from unwanted light reflections, particularly in high-volume production settings where micron or submicron resolution is required, and the difference between acceptable and unacceptable parts is minimal.
Innovation Solution
A method involving the formation of an aperture through a workpart, passing a coherent light beam through it to create a diffraction pattern, capturing and comparing this pattern to a reference pattern to determine thickness, which provides higher signal-to-noise ratios and is less sensitive to noise from unwanted reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser triangulation is used for thickness measurement, then measurement capability is provided, but noise from unwanted light reflections causes false measurements
Solution Approach 1:
The patent extracts only the transmitted light that passes through the workpart and aperture, discarding reflected light that causes noise. By using a light source positioned to illuminate through the aperture and detecting only the transmitted diffraction pattern, the method eliminates unwanted reflections while maintaining measurement capability.
Solution Approach 2:
The patent introduces an aperture as an intermediary element between the light source and detector. This aperture creates a controlled light path where only light passing through the workpart and aperture reaches the detector, serving as a spatial filter that blocks reflected light paths while allowing transmitted light to create the diffraction pattern.
2Measurement precision
If high resolution thickness measurement is required, then measurement sensitivity is improved, but false positive and false negative measurements increase
Solution Approach 1:
The patent utilizes changes in the diffraction pattern characteristics (analogous to color changes in optical measurements) to detect thickness variations. By analyzing the spatial distribution and intensity patterns of diffracted light, the system can detect micron or submicron thickness changes without the false measurements that plague reflected light methods.
3Ease of operation
If optical measurement methods are used, then non-contact measurement is achieved, but sensitivity to light noise from reflections increases
Solution Approach 1:
The patent converts the diffraction phenomenon, which could be considered a distortion of the light path, into a beneficial measurement mechanism. The diffraction pattern created by light passing through the aperture contains encoded information about the workpart thickness, and analyzing this pattern provides accurate measurements while inherently filtering out reflected light noise.
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 method enables highly accurate and robust thickness measurements, ensuring consistent production quality by reducing false positives and negatives, meeting stringent quality control standards of less than one or two defective parts per million.
Implementation Method 1
passing a light beam through the aperture to create a light diffraction pattern on the far side of the workpart
Data Source
AI summary
The thickness of a workpart (10) is measured to a high degree of accuracy by passing a coherent light beam (20) through an aperture (16) in the workpart (10). The aperture (16′) can alternatively be created between an edge of the workpart (10) and an external reference plate (30). The light is diffracted on the far side of the workpart (10) and its diffraction pattern captured by a CCD camera (22). The captured image is analyzed by a computer (24) which compares the captured diffraction pattern to a stored referenced value to determine whether the thickness of the workpart (10) is within an acceptable range. The method is capable of returning measurements with micron or submicron resolution, and is a robust process readily adaptable to high volume production quality control applications.