Eye Tracking Camera Positioning in Head-Mounted Displays
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Solution Overview
Problem
Traditional eye-tracking systems in head-mounted displays face challenges such as increased device size, obstructed camera views due to the nose, and optical distortions, leading to inaccurate tracking and image quality issues.
Innovation Solution
The implementation of a tracking system with optimised camera positioning, where cameras are placed on the periphery of the eye piece at angles between 0 to 40 degrees relative to the horizon plane, minimizing obstruction and improving visibility of eye features, allowing for more accurate gaze tracking without the need for a hot mirror, thus reducing optical distortions and enabling compact device design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the hot mirror is arranged at an angle of 40-70 degrees between the eye piece lens and display, then the camera can capture images of the user's eye, but the overall size of the display device is significantly increased
Solution Approach 1:
The patent removes the hot mirror from the optical path entirely, extracting this problematic component that caused both size increase and optical distortions. The eye tracking camera now captures images directly through the eye piece lens without requiring the hot mirror's reflective surface, thereby eliminating the need for the 40-70 degree angular arrangement that expanded device volume.
Solution Approach 2:
The camera is repositioned to a different spatial dimension - specifically to the periphery of the eye piece lens rather than requiring the traditional arrangement between the lens and display. This dimensional change allows the camera to access the user's eye through the lens edge without needing the hot mirror's angular reflection path, thus reducing device size while maintaining tracking functionality.
2Volume of moving object
If advanced optics are introduced to reduce the distance between the eye piece lens and display, then the device size is reduced, but it becomes impossible to locate the hot mirror at a specific angle and the camera outside the user's field of view
Solution Approach 1:
The hot mirror is completely removed from the system, eliminating the constraint it imposed on camera positioning. With the hot mirror extraction, the camera can be freely positioned at the periphery of the eye piece lens without needing to maintain specific angular relationships, enabling compact optical chamber design while preserving eye tracking capability.
Solution Approach 2:
The optical path is segmented into independent functional zones: the eye piece lens maintains its primary function of delivering visual content to the user, while the eye tracking camera operates independently at the periphery to capture eye images. This segmentation removes the interdependence that previously required the hot mirror for spatial separation, allowing compact integration.
3Volume of moving object
If the hot mirror is not arranged to cover the complete field of view, then device size is reduced, but defects such as image uniformity deviation and image distortions are introduced
Solution Approach 1:
The hot mirror is removed entirely, eliminating the source of image uniformity deviations and distortions that occurred at its edges. The eye tracking camera now captures images directly through the eye piece lens without encountering the hot mirror's reflective surface, thereby achieving high image quality without requiring the hot mirror to cover the complete field of view.
4Ease of operation
If the eye piece lens has a specific shape to accommodate the user's nose, then user comfort is improved, but the field of view of the camera is obstructed
Solution Approach 1:
The camera is repositioned to the periphery of the eye piece lens, utilizing the edge region that does not obstruct the user's nose area. This spatial relocation to a different dimension allows the nose-accommodating shape of the eye piece lens to maintain user comfort while the camera at the periphery captures unobstructed images of the user's eye for accurate tracking.
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 solution enhances the accuracy and precision of eye tracking, reduces device size, and maintains image quality by minimizing obstructions and optical distortions, facilitating the use in compact display devices with improved manufacturing efficiency.
Implementation Method 1
the camera 102 captures images of the user's eye through the hot mirror 104... light reflecting off the user's eye passes through the eye piece lens 108
Implementation Method 2
light reflecting off the user's eye passes through the eye piece lens 108 and gets reflected by the hot mirror 104 towards the camera 102
Implementation Method 3
multiple illuminators are employed for emitting light towards the user's eyes, and multiple cameras are employed for capturing images depicting the user's eyes and reflections of the emitted light
Data Source
AI summary
A tracking system for use in a display device that has an eye piece per eye. The tracking system includes a plurality of illuminators per eye, arranged along a periphery of the eye piece; and a first camera per eye, arranged at the periphery of the eye piece. A line passing through the first camera and an optical centre of the eye piece forms a first angle lying in a range of 0 degree to 40 degrees with respect to a horizon plane, wherein an optical axis of the eye piece and an inter-optical horizon line lie on the horizon plane, the inter-optical horizon line passing through optical centres of both eye pieces of the display device. The first camera is positioned below the horizon plane.