Automated Optical Inspection for Scratch and Dig Grading
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Solution Overview
Problem
The existing MIL-PRF-13830B performance specification for inspecting optical components relies on subjective human visual inspection, leading to inconsistent grading and errors in imperfection assessment, particularly in the manufacture and distribution of derivative master sets, which can result in incorrect imperfection numbers being assigned to optical components.
Innovation Solution
A computer-automated test apparatus and method that uses a dark-field microscope to obtain digital images of components, process them to identify scratches and digs, and calculate scratch and dig numbers based on pixel intensity and morphology, replicating the visibility assessment of expert human inspectors, ensuring consistent and reproducible results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If human visual inspection is used to grade scratches and digs, then the inspection can be performed with simple equipment, but the grading becomes subjective and inconsistent
Solution Approach 1:
The patent replaces the human visual inspection system with an automated optical measurement system. A camera captures images of scratches and digs under controlled lighting conditions, and image processing algorithms automatically measure their characteristics. This substitution eliminates subjectivity while maintaining the simplicity of the inspection setup, as the automated system requires only standard optical components rather than complex equipment.
Solution Approach 2:
The patent creates digital copies (images) of the physical imperfections for analysis. By capturing scratches and digs as digital images and measuring their pixel characteristics, the system replicates the human inspection process objectively. The digital measurements of intensity, area, and shape provide consistent, repeatable results that directly correspond to the visual appearance graded by inspectors.
2Productivity
If derivative master sets are manufactured using human grading, then production can proceed with existing reference components, but errors in imperfection numbers are introduced
Solution Approach 1:
The patent implements a feedback mechanism where automated measurements of reference components are compared against established grade boundaries. The system continuously verifies that derivative master sets are accurately graded by measuring their scratch and dig characteristics and confirming they fall within the correct grade ranges. This feedback loop prevents propagation of grading errors through the supply chain.
Solution Approach 2:
The patent replaces human grading of derivative master sets with automated optical measurement. By using camera-based imaging and digital analysis, the system objectively determines the grade of reference components, eliminating the errors introduced by subjective human assessment while maintaining the ability to produce multiple reference sets.
3Measurement precision
If automated optical measurement is used to inspect scratches and digs, then grading consistency is improved, but the equipment complexity increases
Solution Approach 1:
The patent divides the inspection system into separate functional modules: illumination subsystem, imaging subsystem, and measurement subsystem. Each module performs a specific function and can be independently optimized or replaced. The illumination system provides controlled lighting, the camera captures images, and software algorithms analyze the data. This segmentation reduces overall complexity by allowing each component to be simple while working together to achieve consistent measurement.
Solution Approach 2:
The patent controls the optical parameters (lighting conditions, camera settings, magnification) to standard values that replicate the human eye's viewing conditions. By fixing these parameters, the system achieves measurement consistency without requiring complex adaptive control mechanisms. The standardized parameters allow simple, repeatable measurements that are easy to implement and maintain.
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 automated system consistently mimics the subjective grading of expert human inspectors, providing reliable and reproducible assessments of scratches and digs, addressing the inconsistencies and subjectivity of the original human-based inspection method.
Implementation Method 1
the capture of scattered light from the optical surface with the inspector's (human) eye positioned at a defined distance from the test and reference components
Data Source
AI summary
An inspection method for optical components that can be implemented to conform to performance specification MIL-PRF-13830 in order to grade surface imperfections, in particular scratches and digs. A dark-field microscope obtains a digital image of the component, and this digital image is processed to determine scratch and dig numbers. For scratches, the number is obtained by dividing the total intensity of the scratch by the scratch length. For digs, the number is obtained by determining dig diameter or by dividing the dig's total intensity by its area. According to our extensive testing, this automated digital image processing approach appears to faithfully mimic the subjective impression that a scratch makes on an expert inspector who is applying the visibility test of MIL-PRF-13830.