Freeform Waveguide Prism for Ergonomic HMD
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Solution Overview
Problem
Existing head-mounted display (HMD) designs are cumbersome and heavy, preventing widespread acceptance due to their helmet-like form factor, which causes fatigue and discomfort, and lack the ability to provide a wide, minimally blocked see-through field of view essential for daily tasks.
Innovation Solution
The development of a waveguide prism with freeform optical surfaces optimized for ergonomic fit, allowing an eyeglass-like appearance and a wide see-through field of view, using multiple reflections to extend the optical path length and accommodate the human head shape, combined with a compensation lens to correct ray shifts and distortions, enabling a lightweight and non-intrusive HMD design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If traditional waveguide prism designs are used, then the HMD can provide virtual image display, but the device becomes heavy and helmet-like, causing user fatigue and discomfort
Solution Approach 1:
The waveguide prism employs freeform optical surfaces with curved geometries that conform to the natural contours of the human head and face. This curvature allows the device to wrap around facial features rather than protruding outward, distributing weight more evenly and eliminating the helmet-like appearance that causes fatigue.
2Weight of moving object
If the HMD design is made lightweight and compact, then ergonomic comfort improves, but the see-through field of view becomes blocked or degraded
Solution Approach 1:
The freeform waveguide prism utilizes three-dimensional freeform surfaces that manipulate light paths in multiple dimensions. This allows the optical system to provide a wide see-through FOV without requiring large physical dimensions that would block the user's view of the real world or increase device weight.
3Weight of moving object
If freeform surfaces are introduced to reduce system weight, then lightweight HMD design is achieved, but manufacturing complexity increases
Solution Approach 1:
The freeform surfaces are defined by mathematical parameterizations that can be directly translated into manufacturing instructions for modern fabrication processes. This approach balances optical performance requirements with manufacturability, allowing complex curved surfaces to be produced with appropriate precision through computational design methods.
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 provides a lightweight, ergonomic, and eyeglass-like HMD design with a significantly larger see-through field of view, reducing user fatigue and enhancing usability by matching the optical system's shape to the human head, while maintaining superior performance and image quality.
Implementation Method 1
When light propagating through the waveguide prism, if Total Internal Reflection (TIR) condition on a reflective surface is satisfied, the light loss through the reflection is minimal.
Implementation Method 2
Light rays emitted from the image display unit are injected into the waveguide prism via the first refractive surface of the prism. The injected rays propagate through the waveguide prism via multiple reflections and are then coupled out of the prism via the second refractive surface of the prism.
Data Source
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AI summary
This invention concerns an ergonomic optical see-through head mounted display device with an eyeglass appearance. The see-through head-mounted display device consists of a transparent, freeform waveguide prism for viewing a displayed virtual image, a see-through compensation lens for enabling proper viewing of a real-world scene when combined together with the prism, and a miniature image display unit for supplying display content. The freeform waveguide prism, containing multiple freeform refractive and reflective surfaces, guides light originated from the miniature display unit toward a user's pupil and enables a user to view a magnified image of the displayed content. A see-through compensation lens, containing multiple freeform refractive surfaces, enables proper viewing of the surrounding environment, through the combined waveguide and lens. The waveguide prism and the see-through compensation lens are properly designed to ergonomically fit human heads enabling a wraparound design of a lightweight, compact, and see-through display system.