Light Guide Device Hard Coat Coating Uniformity
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Solution Overview
Problem
Existing light guide devices for virtual image display apparatuses, such as head-mounted displays, face challenges in maintaining satisfactory light guiding performance due to complications in coating processes, particularly with non-uniform surfaces, leading to liquid drooping and hard coat failures.
Innovation Solution
A light guide device with a nonaxisymmetric curved surface and a connection portion that connects optical surfaces with a non-uniform height difference, preventing large stepped portions and ensuring a hard coat layer is formed without liquid pooling, using a coating liquid application process that controls the flow of the coating liquid to suppress drooping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hard coat layer is provided on the light guide plate to prevent damage and dirt, then the protective function is improved, but liquid drooping and hard coat failure occur on complicated curved surfaces
Solution Approach 1:
The invention applies local quality by providing the hard coat layer only on specific surfaces (first and second surfaces) of the light guide plate that require protection, while leaving other surfaces without hard coat. This selective coating approach ensures protective function is provided where needed while avoiding coating defects on complicated curved surfaces.
Solution Approach 2:
The invention segments the coating process by dividing the light guide plate into multiple surfaces and selectively applying hard coat to specific surfaces (first and second surfaces) rather than coating the entire plate. This segmentation prevents liquid drooping issues that would occur on complicated curved surfaces while maintaining protective function on critical surfaces.
2Reliability
If the light guide plate has a complicated shape with multiple curved surfaces to achieve optical functionality, then the optical performance is improved, but the coating process becomes difficult and liquid drooping occurs
Solution Approach 1:
The invention applies local quality by selectively providing the hard coat layer only on the first and second surfaces of the light guide plate that require both optical functionality and protection. This approach maintains the complicated shape needed for optical performance while avoiding coating difficulties on other complicated curved surfaces by leaving them without hard coat.
3Area of stationary object
If coating liquid is applied to complicated curved surfaces, then complete coverage is intended, but the coating liquid converges to a single point and droops on the surface
Solution Approach 1:
The invention applies local quality by selectively providing the hard coat layer only on the first and second surfaces of the light guide plate, avoiding application on complicated curved surfaces where liquid drooping would occur. This ensures uniform coating on selected surfaces while maintaining complete coverage where hard coat is provided.
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 solution effectively maintains satisfactory light guiding performance by preventing liquid drooping and ensuring a uniform hard coat layer, even on complex surfaces, thereby enhancing the reliability and precision of video image light guidance and see-through functionality.
Implementation Method 1
guides the video image light through internal reflection to cause the video image light to exit out of the light guide device
Data Source
AI summary
In a light guide device, a step between optical surfaces connected to each other by a connection portion can be limited (e.g., to 1 mm or smaller) so that a large stepped portion is not allowed to be formed at the connection portion in a hard coat formation process, whereby a coating liquid that flows along portions that are to form the optical surfaces forms no liquid pool or causes no liquid sagging. The light guide device can thus maintain satisfactory light guiding performance at the light guide portion.