Contact Lens Defect Analysis Using Dual Illumination
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Solution Overview
Problem
Current manual inspection systems for contact lenses are tedious and prone to errors when identifying and classifying defects, especially when using optical comparators, leading to inaccuracies in defect representation and potential time-consuming corrections in the manufacturing process.
Innovation Solution
A contact lens defect analysis system incorporating high-resolution cameras, dual illumination modules (Bright Field and Dark Field) with a beam splitter for aberration-free imaging, and a large viewing screen for accurate defect classification, allowing operators to capture specific defect areas and store images with detailed parameters like lot traceability and measurement data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If automated inspection systems are used to identify and classify defects in contact lenses, then productivity is improved, but measurement precision and reliability of defect detection deteriorate
Solution Approach 1:
The inspection system is divided into multiple specialized modules: bright field illumination module for detecting surface defects, dark field illumination module for detecting subsurface defects, and separate camera systems for different defect types. This segmentation allows each module to specialize in detecting specific defect characteristics, improving overall measurement precision while maintaining automated productivity.
Solution Approach 2:
A beam splitter is introduced as an intermediary optical element that directs light from a single source to both bright field and dark field illumination paths simultaneously. This intermediary component enables dual illumination modes without requiring separate light sources, maintaining productivity while enhancing defect detection capability through multiple illumination techniques.
2Measurement precision
If manual inspection with optical comparators is used, then measurement precision is improved, but productivity deteriorates and time is lost
Solution Approach 1:
The system creates optical copies (images) of the contact lens under different illumination conditions using high-resolution cameras. These digital copies preserve the detailed visual information that operators need for precise defect classification, while enabling automated processing and eliminating the need for manual viewing through optical comparators, thus improving productivity without sacrificing measurement precision.
Solution Approach 2:
The manual mechanical inspection process using optical comparators is replaced with an automated optical-mechanical system that uses programmable illumination modules, beam splitters, and digital image processing. This substitution maintains the detailed visualization capability needed for precise defect detection while eliminating the time-consuming manual operation, thereby improving productivity.
3Device complexity
If only bright field illumination is used in manual inspection systems, then device complexity is reduced, but measurement precision deteriorates due to inability to detect certain defect types
Solution Approach 1:
A single illumination system is designed to perform multiple functions by incorporating both bright field and dark field illumination capabilities. The system can switch between or simultaneously operate in both illumination modes using a beam splitter, enabling detection of various defect types (surface scratches, subsurface bubbles, staining) without requiring multiple separate illumination devices, thus maintaining reasonable complexity while improving measurement precision.
Solution Approach 2:
The illumination system allows dynamic change of illumination parameters (brightness, direction, angle) to optimize defect detection for different defect types. By adjusting these parameters, the system can transition between bright field and dark field modes to reveal different defect characteristics, improving measurement precision without significantly increasing device complexity.
4Measurement precision
If the entire contact lens image is stored at full resolution, then measurement precision is maintained, but loss of substance increases due to excessive data storage requirements
Solution Approach 1:
The system extracts and stores only the relevant defect regions from the full contact lens image at full resolution, rather than storing the entire image. By identifying and isolating defect areas using the dual illumination system and then storing only these extracted regions, the system maintains measurement precision for defect analysis while significantly reducing data storage requirements.
Solution Approach 2:
The image data is segmented into defect regions and non-defect regions. Only the defect regions are stored at full resolution for detailed analysis, while the rest of the image is either discarded or stored at lower resolution. This segmentation approach preserves measurement precision for critical defect areas while reducing overall data storage 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
Enhances the accuracy and efficiency of defect classification and measurement, reducing errors and streamlining the correction process by providing clear, magnified images with precise defect analysis and storage of specific defect areas, enabling better optimization of manufacturing processes.
Implementation Method 1
an aberration free image of the contact lens is captured at an intermediate stage by using a beam splitter
Implementation Method 2
The Dark field light head illuminates the bottom of the lens to produce a Dark field image of the lens
Implementation Method 3
a second lighting module namely the Bright field light head illuminates the lens to produce a bright field image of the lens
Data Source
AI summary
A manual inspection system and method to inspect for defects in Contact lenses comprising; an image acquisition system with at least two high resolution cameras; Top illumination light head used for acquiring Bright field images; a Backlit illumination module to acquire Dark field images; at least another back lit illumination module to acquire a different type of Bright field images; an interchangeable mechanism to change measurement gauges suitable for a particular product; a rotating wheel embedded with multiple optical filters to cater to different imaging requirements; a first camera to capture the full view of the contact lens at a beam splitter; a second camera suitably mounted on a swivel arm to capture a higher resolution image of a selected defective area as viewed on a projection screen; a glass template or measurement gauge mounted at a suitable position to achieve overlaid images of the lens and the gauge on a projection screen for taking measurements; a flexible template measurement gauge as an optional overlay, to replace the glass template, suitably mounted on the projection screen for easy measurement of defects and geometry of the contact lens; an XYZ table to position the contact lens; creating a database on the computer that tabulates geometrical information and detailed defect information along with their respective positional information; and subsequently analyzing the database images to arrive at corrective actions to the manufacturing process to improve the quality and yields in the contact lens.