HMD Illumination Diffusion Plate Positioning
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Solution Overview
Problem
Head-mounted displays (HMDs) face challenges in achieving high efficiency, high brightness, and downsizing while preventing the generation of conjugate images when using a microlens array, which affects image visibility and optical system size.
Innovation Solution
The HMD incorporates a microlens array illuminated by a light source unit, a condensing optical member to focus light on the display unit, and a diffusion plate positioned closer to the condensing optical member than the microlens array to prevent conjugate image formation, ensuring high brightness and compact size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a microlens array is adopted in an illumination unit to increase efficiency and brightness, then optical efficiency and brightness are improved, but a conjugate image is formed on the exit pupil which disturbs the displayed image
Solution Approach 1:
The patent extracts the harmful conjugate image formation by introducing a diffusion plate that scatters light before it can form the conjugate image on the exit pupil. This separates the useful light transmission function from the harmful conjugate image generation, allowing the microlens array to maintain its efficiency benefit while the diffusion plate eliminates the disturbance.
Solution Approach 2:
The diffusion plate acts as an intermediary element between the microlens array and the exit pupil. It intercepts the light paths that would otherwise converge to form the conjugate image and scatters them instead, preventing the harmful effect while preserving the beneficial light transmission through the microlens array.
2Object-affected harmful factors
If a light guide plate is used to maintain see-through nature, then visibility of external environment is improved, but optical efficiency is deteriorated
Solution Approach 1:
The patent applies local quality by using a diffusion plate with specific scattering properties at a critical location in the optical path. The diffusion plate provides localized light scattering only where needed to prevent conjugate image formation, while maintaining overall optical efficiency and the see-through nature provided by the light guide plate.
3Volume of moving object
If optical system size is reduced for compact HMD design, then wearability is improved, but achieving high brightness becomes more difficult
Solution Approach 1:
The patent employs nesting by integrating the diffusion plate within the existing compact optical structure, placing it in close proximity to the microlens array and condensing optical member. This nested arrangement prevents conjugate image formation without adding significant volume, allowing the system to maintain both compact size and high brightness performance.
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
This configuration enhances the visibility of the displayed image by inhibiting conjugate image generation, achieving a high-brightness, efficient, and compact optical system for HMDs, improving user experience and wearability.
Implementation Method 1
a microlens array that is illuminated by light emitted from the light source unit and becomes a virtual secondary light source
Implementation Method 2
a condensing optical member to focus light from the microlens array on the display unit
Implementation Method 3
a diffusion plate to diffuse light from the microlens array
Implementation Method 4
a light guide unit to transmit image light from the projection unit to the pupils of the user
Data Source
AI summary
A head mounted display has a display unit to generate a displayed image, an illumination unit to emit illumination light to the display unit, a projection unit to project image light from the display unit, and a light guide unit to transmit image light from the projection unit to pupils of a user. Here, the illumination unit has light source units, a microlens array that is illuminated by light emitted from the light source units and becomes a virtual secondary light source, a condensing optical member to focus light from the microlens array on the display unit, and a diffusion plate to diffuse light from the microlens array, and the diffusion plate is arranged closer to the condensing optical member than to the microlens array. As a result, a conjugate image is inhibited from being generated with the adoption of a microlens array.