Dual-Material Ophthalmic Lens Blanks for Deformation-Free Machining
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Solution Overview
Problem
Current methods for manufacturing ophthalmic lenses face challenges such as deformation due to cutting and clamping forces, high production costs, and inefficiencies in work holding methods that require additional operations and materials, leading to suboptimal mechanical stability and material waste.
Innovation Solution
The use of plastic circular blanks composed of two different materials, where a high-quality transparent plastic forms the lens element surrounded by a less expensive plastic ring fixture, allowing for optimized thickness without the drawbacks of existing methods, enabling machining of both sides and reducing material waste by using the cheaper material for the rim region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the lens is clamped on its outside diameter during machining, then the lens can be held securely, but the clamping pressure causes deformation of the work piece affecting optical properties
Solution Approach 1:
A mounting device is introduced as an intermediary between the clamping system and the lens. The mounting device includes a mounting surface that contacts the lens at the optical center and a clamping surface that receives clamping forces, thereby mediating the transmission of clamping forces away from the lens to prevent deformation while maintaining secure holding.
Solution Approach 2:
The mounting device separates the functions of optical contact and mechanical clamping into distinct surfaces: a mounting surface for optical center contact and a clamping surface for force application. This segmentation allows the lens to be clamped securely without the clamping pressure affecting its optical properties.
2Weight of moving object
If thickness optimization is applied to minimize lens weight, then the lens becomes lighter, but the rigidity of the lens decreases making it difficult to locate, clamp and machine
Solution Approach 1:
The mounting device acts as a counterbalancing structure that compensates for the reduced rigidity of the optimized lens. By providing a rigid mounting surface at the optical center and extending clamping surfaces, the mounting device counteracts the flexibility introduced by thickness optimization, enabling secure location and clamping without compromising the weight benefits.
3Measurement precision
If a block is bonded to the lens surface for work holding, then the lens can be accurately fixed, but additional operations are required including coating the surface with protective film and removing the block later
Solution Approach 1:
The mounting device combines multiple functions into a single integrated component: it provides accurate fixing through the mounting surface, protects the optical surface by distributing forces away from it, and serves as a permanent fixture that eliminates the need for separate blocking and unblocking operations. The mounting device merges the functions of the block, protective film, and clamping mechanism into one structure.
4Ease of operation
If radial clamping is applied directly to the lens, then the lens can be held in place, but the pressure from the clamping chuck causes deformation of the work piece
Solution Approach 1:
The mounting device serves as an intermediary structure between the clamping chuck and the lens. The clamping surfaces of the mounting device receive the radial clamping forces from the chuck, while the mounting surface at the optical center provides stable positioning. This intermediary arrangement enables easy work holding operations while preventing direct transmission of clamping pressure to the lens that would cause deformation.
Data Source
AI summary
For manufacturing ophthalmic lenses and other optical form bodies made of plastic material, plastic form parts are used which are made by non-cutting shaping and are then further worked by mechanical production steps. Said plastic form parts are circular blanks (1) made of two different plastic materials which are firmly joined to each other. Thereby, an interior lens element (2) that consists of a high-quality material is concentrically surrounded by a ring fixture (3) which consists of a low priced material. Either surface of the lens element (2) may feature any given geometry. During mechanical working, the ring fixture (3) is used for mounting as well as for depositing and, in addition, for stabilizing the workpiece (9). For this reason it is partially maintained throughout the mechanical working and is cut off at the end only.