One-Piece Shield Freeform Geometry for Prism Control
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Solution Overview
Problem
Conventional one-piece shields for unitary-lens eyeglasses and safety helmets often fail to balance aesthetic and optical requirements, leading to prismatic distortions and discomfort due to non-zero prism imbalance and optical power issues, especially when wrapped and tilted.
Innovation Solution
A non-corrective unitary lens eyeglasses and safety helmet design featuring a one-piece shield with a freeform surface geometry, mounted in a frame that maintains a predetermined local relationship with the wearer's head, achieving non-zero minus power and prism as worn of less than 0.15 prism diopter, optimized for various standardized head models to minimize distortion and discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional one-piece shields are wrapped and tilted to fit standardized head models, then aesthetic and fit requirements are met, but prismatic distortions and optical discomfort occur due to non-zero prism imbalance
Solution Approach 1:
The patent applies local quality by implementing a freeform surface geometry on the shield that provides different optical properties in different zones. The surface is designed with varying curvature and orientation across the shield area, allowing each local region to compensate for the specific prismatic effects experienced at that location when the shield is wrapped and tilted on the head. This localized optimization eliminates the need for uniform geometric corrections and achieves minimal prism imbalance across the entire visual field.
Solution Approach 2:
The patent employs parameter changes by systematically varying the surface parameters (curvature, orientation, asphericity) of the shield throughout its extent. The freeform surface is defined by mathematical functions that control how these geometric parameters change across different locations on the shield. By carefully adjusting these parameters, the design compensates for the prismatic effects introduced by wrapping and tilting, achieving optimal optical performance while maintaining aesthetic shape requirements.
2Object-affected harmful factors
If the shield uses freeform surface geometry to minimize prism imbalance, then optical comfort is improved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces complex multi-step mechanical manufacturing processes with a single injection molding operation. The freeform surface geometry, which would traditionally require multiple precision machining, grinding, and polishing steps, is instead created directly in the mold cavity. This substitution of mechanical fabrication with mold-based manufacturing significantly reduces production complexity, time, and cost while maintaining the precision of the freeform surface.
Solution Approach 2:
The patent changes the manufacturing approach from mechanical fabrication to injection molding, fundamentally altering the process parameters. Instead of controlling tool paths, feed rates, and removal rates associated with mechanical machining, the design leverages mold cavity geometry, material flow characteristics, and curing parameters. This parameter transformation enables the production of complex freeform surfaces with simpler, more scalable processes suitable for mass production.
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 design effectively reduces prismatic distortions and discomfort by establishing a freeform surface geometry that maintains optimal optical properties across different head models, ensuring comfort and accurate visual perception.
Implementation Method 1
the one-piece shield being disposed in the predetermined local relationship with respect to the wearer's head and eyes establishing non-zero minus power and prism as worn of less than 0.15 prism diopter
Data Source
AI summary
The invention is directed to non-corrective unitary lens eyeglasses and safety helmets including a one-piece shield and a method for making such a one-piece shield. The method is for designing a one-piece shield for non-corrective unitary lens eyeglasses or a safety helmet, whereby the shield has a front and a back surface, and is computer-implemented with the steps: providing a front surface geometry of the shield; providing a local relationship of the front surface geometry with respect to a center of rotation of a wearer's eye; and, calculating a portion of a back surface geometry attributed to the wearer's eye by establishing non-zero minus power and minimizing prism. The portion of the back surface geometry is a freeform surface geometry.