Spectacle Lens Peripheral Lentic Zone for Edge Thickness
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Solution Overview
Problem
The manufacturing of spectacle lenses with positive spherical prescriptions faces challenges in achieving a thin center thickness while maintaining a sufficient edge thickness, as the thickness at the geometric center increases with diameter, leading to heavier and less preferred lenses for wearers.
Innovation Solution
A finished uncut spectacle lens design featuring a curved front surface with a convex optical bowl and a peripheral lentic zone, where the curvature in the lentic zone deviates from the optical bowl, allowing for a large uniform circular crib shape without increasing the complexity of the back surface machining, enabling a sufficient edge thickness without thickening the lens center.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the diameter of the finished uncut spectacle lens is increased to provide a sufficient cribbed edge thickness for handling and manufacturing, then the edge thickness is improved, but the center thickness increases leading to heavier lenses
Solution Approach 1:
The patent applies local quality by creating a peripheral lentic zone with different curvature characteristics than the optical bowl. The front surface has a first curvature in the optical bowl and a second curvature in the peripheral zone, allowing the edge thickness to be increased locally without affecting the center thickness. This enables the lens to have sufficient edge thickness for handling while maintaining thin center thickness for light weight.
Solution Approach 2:
The patent utilizes the curvature dimension of the front surface to control thickness distribution. By varying the curvature radius in different zones (first curvature radius in optical bowl, second curvature radius in peripheral zone), the lens achieves different thickness profiles in different radial dimensions, allowing independent optimization of edge and center thickness.
2Reliability
If the diameter of the finished uncut spectacle lens is increased to allow removal of coating defects during edging, then coating quality is improved, but the lens center thickness and weight increase
Solution Approach 1:
The peripheral lentic zone provides an extended annular region where coating defects can be removed during edging without affecting the optical performance area. This local extension of the lens periphery allows for quality control while maintaining the optical bowl dimensions that determine center thickness and weight.
3Ease of manufacture
If a large uniform circular crib shape is used to simplify manufacturing and handling, then ease of manufacture is improved, but the lens center thickness increases
Solution Approach 1:
The patent maintains a uniform circular crib shape for ease of manufacturing and handling, but uses local curvature variation in the peripheral lentic zone to control thickness distribution. This allows the simplified circular shape to be maintained while preventing the center thickness from increasing proportionally with the overall diameter.
Data Source
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AI summary
A finished uncut spectacle lens (20) is provided. The spectacle lens (20) includes a curved front surface (21) including an optical bowl (15) with a convex curvature and a peripheral lentic zone (27) surrounding the optical bowl (15). The curvature of the curved front surface (21) in the peripheral lentic zone (27) is flatter than in the optical bowl (15). The optical bowl size is large enough that a lens filling the entire frame can be glazed from it. The inclusion of a flatter peripheral lentic zone enables a larger diameter of the finished unglazed lens (d) with larger edge thickness (29) than would be possible if the same back surface was cut on a semi-finished blank having a uniform spherical front (30), without compromise to the finished lens center thickness (32). In addition, a method of manufacturing such a spectacle lens (20) and a semi-finished lens blank used in the method are provided.