Freeform Prism Gaze Tracking in See-Through Head-Mounted Displays
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Solution Overview
Problem
Near-eye display systems that utilize waveguides are sensitive to eye movement, leading to distortion in gaze-tracking accuracy due to changes in the distance between the eye and the display components, as the gaze-tracking system is not object-space telecentric.
Innovation Solution
The implementation of a freeform prism in the near-eye display system allows the display and gaze-tracking system to share optics, positioning the gaze-tracking system at the back focal plane of the freeform prism, which maintains accuracy by keeping the eye image collimated and focused, reducing sensitivity to eye movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the gaze-tracking system shares optics with the display system in a near-eye display, then the device complexity is reduced and the structure becomes more compact, but the system becomes sensitive to eye movement causing distortion in gaze-tracking accuracy
Solution Approach 1:
The patent introduces a telecentric optical design that adds a dimensional constraint to the light paths, ensuring that all rays entering the imaging sensor are parallel to the optical axis. This dimensional constraint (telecentricity) resolves the contradiction by maintaining measurement precision across varying eye positions while still allowing shared optics between display and gaze-tracking systems
Solution Approach 2:
The patent changes the optical parameters by positioning the imaging sensor at the back focal plane of the freeform prism and designing the illumination optics to create object-space telecentricity. This parameter change (sensor positioning at focal plane) transforms the system from being sensitive to eye movement to being robust against such movements, maintaining gaze-tracking accuracy while using shared optics
2Adaptability or versatility
If the distance between the user's eye and display components changes due to eye movement, then the system becomes more adaptable to natural eye motion, but the gaze-tracking accuracy deteriorates due to perspective errors and distortions
Solution Approach 1:
The patent creates an equipotential optical environment by implementing object-space telecentricity, where the chief rays are parallel to the optical axis across the entire field of view. This ensures that all eye positions within the acceptable range are optically equivalent, eliminating perspective errors and maintaining consistent gaze-tracking accuracy regardless of eye movement or distance changes
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 ensures accurate gaze direction determination regardless of changes in the distance between the eye and the display system, reducing perspective errors and distortions, thus maintaining precise gaze tracking.
Implementation Method 1
a freeform prism, a display device configured to emit display light through the freeform prism to an eye of a user, and an imaging device configured to receive gaze-detection light reflected from the eye and directed through the freeform prism
Implementation Method 2
an illumination prism through which display light is emitted and gaze-detection light is emitted and received
Data Source
AI summary
An example see-through head-mounted display system includes a freeform prism and a display device configured to emit display light through the freeform prism to an eye of a user. The see-through head-mounted display system may also include an imaging device configured to receive gaze-detection light reflected from the eye and directed through the freeform prism.