Eyewear Display Offset Adhesive Bonding
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Solution Overview
Problem
Existing eyewear devices with multi-layered displays face stress issues due to adhesive bonding at the edges, leading to bending stress and poor drop test performance, which affects product reliability.
Innovation Solution
The use of an offset adhesive bonding method where the adhesive is positioned inward from the outer edge of the display layers, eliminating bending moments and stress at the waveguide edges, and ensuring a simply supported structure that minimizes stress during bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive bonding is performed at the edges of the display layers, then the layers are securely bonded together, but bending stress and stress concentration occur at the waveguide edges leading to poor drop test performance
Solution Approach 1:
The adhesive bonding is applied selectively at specific locations rather than uniformly across the entire edge. The offset distance positions the adhesive away from the outermost edge, creating a local quality distinction where the edge region remains stress-free while the bonding function is maintained at the offset position.
Solution Approach 2:
Instead of bonding at the outer edge to maximize bonding area, the invention inverts the approach by bonding at an offset position inward from the edge. This counterintuitive positioning eliminates bending moments at the edge while maintaining sufficient bonding strength through the offset adhesive application.
2Area of stationary object
If adhesive is positioned at the outer edge of the display layers, then maximum bonding area is achieved, but bending moments create stress concentration at the waveguide edges
Solution Approach 1:
The bonding function is localized to a specific offset position rather than distributed across the entire edge. This creates a local quality where the offset region provides bonding while the edge region remains free of adhesive-induced stress concentration.
Solution Approach 2:
The position parameter of the adhesive is changed from the outer edge to an offset distance inward. This parameter change transforms the stress distribution by eliminating bending moments at the edge while maintaining adequate bonding area at the new offset position.
3Stability of the object's composition
If the display structure is bonded at the edges, then structural stability is provided, but stress concentration leads to edge breakage during impacts
Solution Approach 1:
The offset adhesive positioning acts as a preventive measure by eliminating stress concentration at the edge before impact occurs. This beforehand design choice cushions the edge region from stress-induced damage during subsequent drops or impacts.
Solution Approach 2:
The invention converts the potential harm of edge stress concentration into a benefit by using the offset adhesive position. The offset positioning transforms what would be a stress concentration zone into a stress-free zone, turning a harmful effect into a protective feature.
Data Source
AI summary
Eyewear including a multi-layered display having an adhesive bonding the layers together at an offset distance inward from an outer edge of the layers. The display has an image display layer, such as an optical waveguide in one example, and a pair of layers encompassing the image display layer and which may comprise optically transparent substrates, such as glass. A respective adhesive is positioned the offset distance inward from the outer edge of the display layer between the image display layer and each of the pair of layers to reduce stress in the display. Each of the adhesives may be a continuous bead such that there is no adhesive between the pair of layers and the image display layer at the outer edges. In one example, the offset distance may be at least double the thickness of the image display layer to reduce stress in the image display layer.