Symmetrical Plastic Lens Rib Design for Optical Alignment
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Solution Overview
Problem
Conventional plastic lenses manufactured by injection molding exhibit non-axisymmetric shapes, leading to asymmetric contraction and deformation when assembled in barrels due to uneven press-fitting forces, resulting in errors in optical axis alignment and tilting during assembly.
Innovation Solution
Designing a plastic lens with a symmetrical shape featuring concentric effective aperture and rib portions, including multiple concave portions on the rib's outer surface that are symmetrical and larger than the aperture, reducing contact area and press-fitting force, thereby minimizing shape errors and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional non-axisymmetric lens shape is used, then the lens can be manufactured by standard injection molding, but asymmetric contraction and deformation occur during press-fitting assembly causing optical axis alignment errors
Solution Approach 1:
The patent applies asymmetry in reverse - it introduces symmetric features (concentric circular rib portion and aperture portion) into a lens that would otherwise be asymmetric due to the gate cut. By making the rib portion concentric with the aperture portion and adding symmetric concave portions, the design compensates for the asymmetry introduced by the gate cut, ensuring uniform contraction around the optical axis during press-fitting assembly.
2Ease of operation
If the outer circumferential surface of the rib portion is pressed and fitted into the barrel, then the lens can be assembled, but excessive press-fitting force causes tilting and plastic deformation
Solution Approach 1:
The patent segments the outer circumferential surface of the rib portion by introducing multiple concave portions (at least three) around the circumference. This segmentation reduces the continuous contact area between the lens and barrel, distributing the press-fitting force across multiple smaller contact zones rather than one large continuous zone, thereby reducing excessive force concentration that causes tilting and plastic deformation.
Solution Approach 2:
The concave portions create local variations in the rib portion's outer surface, changing the contact characteristics at specific locations. By having non-contact portions (the concave areas) interspersed with contact portions, the patent creates localized contact zones that reduce overall press-fitting force while maintaining adequate mechanical coupling for assembly.
3Stability of the object's composition
If the rib portion has a large contact area with the barrel, then adequate mechanical coupling is achieved, but excessive press-fitting force is applied causing deformation
Solution Approach 1:
The continuous contact surface is segmented into multiple discrete contact zones separated by concave portions. This segmentation maintains mechanical coupling stability through distributed contact points while reducing the total effective contact area, thereby lowering the overall press-fitting force applied to the lens and preventing shape deformation.
Data Source
AI summary
A lens injection mold includes an upper mold and a lower mold, a cavity provided in the upper mold or the lower mold and having a shape corresponding to the rib portion having the concave portions in order to form the rib portion, and an upper core and a lower core disposed to be movable inside the upper mold and the lower mold and having an upper tip portion and a lower tip portion, respectively, the tip portions having a shape corresponding to the effective aperture portion such that the effective aperture portion is created by pressing injection liquid.