Spectacle Lens Casting via Pilot Rod Segmentation
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Solution Overview
Problem
The existing casting methods for spectacle lenses face challenges such as optical strain, high rejection rates, and wastage due to uneven heat distribution and material shrinkage, particularly in producing thick lenses for high power prescriptions, which require labor-intensive inspection and result in significant material wastage.
Innovation Solution
A process involving the curing of a reactive monomer composition in an elongated mould to form a plastic rod, which is then transversely cut to create spectacle lenses or lens blanks, utilizing a urethane resin with controlled polymerization to avoid striation and reduce wastage, allowing for longer gelation times and improved temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional casting methods are used to produce thick lenses for high power prescriptions, then the lenses can be manufactured, but optical strain occurs due to uneven heat distribution during polymerization
Solution Approach 1:
The invention divides the casting process into two distinct stages: first casting a thin pilot lens to establish uniform thermal properties, then adding the remaining monomer to achieve the final thick lens thickness. This segmentation allows the polymerization to proceed with uniform heat distribution throughout the entire lens volume, preventing optical strain in high power prescriptions.
Solution Approach 2:
The pilot lens is cast and partially polymerized before the remaining monomer is added. This preliminary action creates a structural foundation that ensures uniform thermal conduction during the subsequent polymerization of the full-thickness lens, thereby preventing uneven heat buildup and optical strain.
2Productivity
If conventional casting methods are used, then lenses can be produced, but rejection rates increase due to optical strain and defects
Solution Approach 1:
The process segments lens production into pilot lens casting followed by completion casting, which eliminates optical strain and defects. This results in dramatically reduced rejection rates and improved lens acceptance, directly enhancing reliable productivity by reducing rework and waste.
Solution Approach 2:
The pilot lens serves as a thermal conduit that provides feedback control for heat distribution during the polymerization of the remaining monomer. This ensures uniform temperature distribution throughout the thick lens, preventing optical strain and reducing rejection rates.
3Ease of manufacture
If conventional casting methods are used with flexible gaskets to accommodate shrinkage, then lenses can be produced, but device complexity increases and labor-intensive inspection is required
Solution Approach 1:
The invention extracts the problematic flexible gasket from the mould assembly by using a rigid mould design. The pilot lens casting process creates a structure that accommodates shrinkage without requiring complex flexible components, thereby simplifying the overall device while maintaining ease of manufacture.
Solution Approach 2:
The pilot lens acts as a thermal copy or template that replicates the uniform thermal properties needed for the final lens. This copying approach simplifies the manufacturing process by using the pilot lens to establish optimal thermal conditions without requiring complex active temperature control systems.
4Loss of substance
If conventional casting methods are used, then lenses must be cast in greater thickness to accommodate grinding and fitting, but material wastage increases
Solution Approach 1:
The pilot lens is cast with precise thickness control before the remaining monomer is added. This preliminary action establishes the exact final thickness of the lens, eliminating the need to cast with excessive thickness for subsequent grinding. As a result, material wastage is significantly reduced while maintaining precise thickness control.
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 the production of high-quality spectacle lenses with reduced optical strain and lower rejection rates, minimizing material wastage by allowing for precise control of polymerization and extended gelation times, thereby improving the efficiency and accuracy of lens production.
Implementation Method 1
curing a reactive monomer composition in an elongated mould to form a plastic rod
Implementation Method 2
an exothermic chemical reaction occurs which generally requires cooling of the mould to maintain control of the process
Data Source
Figure 1a~3c
Figure 4
Figure 5
AI summary
A process for preparing spectacle lenses or lens blanks comprising curing a reactive monomer composition in an elongated mould (100a, 100b, 100c) to form a plastic rod for transversely cutting portions therefrom for forming spectacle lenses or spectacle lens blanks.