X-Prism Beamsplitter for Compact HMD Eye Tracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional eye tracking mechanisms in head-mounted display (HMD) systems are hindered by complex optical arrangements that inhibit small form factors and require compute-intensive algorithms, making them impractical for HMD devices without high-performance computing systems.
Innovation Solution
An eye-tracking system utilizing an x-prism beamsplitter positioned between the display panel and the user's eye, combined with an eye-tracking camera capturing composite images of IR light and eye reflections, allows for efficient gaze direction determination without occluding the display and reducing computational demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional eye tracking mechanisms with complex optical arrangements are used, then eye tracking functionality is achieved, but device complexity increases and form factor is enlarged
Solution Approach 1:
The optical path is segmented into separate channels: a first optical path for displaying visual content to the user and a second optical path for capturing eye images. This segmentation allows independent optimization of each path, reducing overall system complexity while maintaining eye tracking functionality.
Solution Approach 2:
A beamsplitter is introduced as an intermediary optical element that directs light from the display panel through a first optical path to the user's eye while simultaneously directing a portion of the light through a second optical path to the eye-tracking camera. This intermediary enables dual functionality without requiring separate complex optical systems.
2Measurement precision
If complex optical mechanisms are used for eye tracking, then gaze direction can be estimated, but the display panel is occluded and form factor increases
Solution Approach 1:
The beamsplitter is designed to reflect only a portion of the display light toward the eye-tracking camera, allowing the majority of light to pass through to the user's eye. This partial action enables eye tracking functionality while minimizing display occlusion and maintaining a compact form factor.
3Measurement precision
If conventional eye tracking algorithms are implemented, then gaze direction is determined, but computational requirements are high and power consumption increases
Solution Approach 1:
The system changes the parameter of light wavelength by using infrared illumination at a wavelength different from the visible display content. This allows the eye-tracking camera to capture eye images in the infrared spectrum, enabling simpler image processing algorithms that are less computationally intensive while maintaining accurate gaze direction determination.
4Reliability
If infrared light sources are positioned close to the display panel, then eye tracking is enabled, but visible light intensity is reduced
Solution Approach 1:
The system applies local quality differentiation by using infrared illumination specifically for eye tracking purposes while keeping the visible display content separate. The beamsplitter and optical paths are designed to handle different wavelengths independently, allowing infrared light sources to be positioned close to the display panel without significantly reducing visible light intensity reaching the user's eye.
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
Enables accurate eye tracking in HMDs with reduced form factors and lower computational requirements, facilitating foveated imaging and user input functionalities while maintaining acceptable visible light intensity and display quality.
Implementation Method 1
causing an image or other representation of the reflection of the light from the user's eye and the area of surrounding the eye to be projected to the eye-tracking camera
Implementation Method 2
The x-prism beamsplitter causes an image or other representation of the light from the display screen and the IR light from the set of IR light sources to be projected to the eye-tracking camera while also concurrently causing an image or other representation of the reflection of the light from the user's eye
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
An HMD device (100, 300) includes a display panel (102, 308, 310) and an x-prism beamsplitter (104) disposed along a first axis (202) between the display panel and an expected position of an eye (112). The x-prism beamsplitter directs a first light beam (212) in a first direction from the display panel to the eye along the first axis, directs a second light beam (216) in a second direction along a second axis (208) substantially perpendicular to the first axis, and directs a third light beam (222) in the second direction along the second axis, wherein the second light beam is representative of the first light beam and the third light beam is representative of a reflection of the first light beam off of the eye. The HMD device further includes an imaging camera (106) to capture a composite image (232) comprising a combination of both a representation of the second light beam and a representation of the third light beam.