Compact Eye Tracking Prism for On-Axis Imaging
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Solution Overview
Problem
Conventional eye tracking devices are bulky, unsightly, and interfere with the user's field of view due to their design, which limits their usability in everyday environments and results in optical performance challenges.
Innovation Solution
A compact eye tracking system using a thin prism to fold the imaging path between the camera and the eye, allowing for on-axis imaging while maintaining a lightweight and aesthetically appealing form factor, and incorporating a corrective optical element to eliminate distortions for unobstructed viewing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the camera is mounted on the eyeglass frame under the eye to directly image the eye, then the device achieves an eyeglass-like appearance, but the frame becomes thick and bulky to move the camera far enough away from the face to avoid interference
Solution Approach 1:
The patent uses a reflective element (beamsplitter or mirror) to fold the optical path, allowing the camera to be positioned in a different spatial dimension (above or to the side of the eyeglass frame) while still capturing eye images. This dimensional repositioning eliminates the need for thick frames while maintaining the eyeglass-like appearance.
2Volume of moving object
If the camera captures an eye image at a close distance and from a slanted direction, then the device maintains a compact form factor, but the eye image suffers from keystone distortion
Solution Approach 1:
The patent introduces a reflective element (beamsplitter or mirror) as an intermediary optical component that redirects light from the eye to the camera. This intermediary enables the camera to capture images from a more favorable angle while maintaining compact dimensions, thereby reducing keystone distortion without sacrificing device compactness.
3Reliability
If a beamsplitter is used to image the eye by a vertically oriented camera, then the arrangement improves over other designs, but the field of view of the camera is severely limited by the disclosed geometry
Solution Approach 1:
The patent employs asymmetric positioning of the reflective element and camera, along with tilted surfaces on the beamsplitter, to expand the field of view. By optimizing the angles and positions asymmetrically, the system captures a wider range of eye movements and positions compared to symmetric or conventional arrangements.
4Reliability
If wide eyeglass lenses are used to avoid interference between the imaging path and any part of the user's face, then the eye image can be captured through reflection off the glass, but the overall package does not resemble a conventional pair of eyeglasses
Solution Approach 1:
The patent uses a dedicated reflective element (beamsplitter or mirror) mounted on the eyeglass frame as an intermediary to redirect light from the eye to the camera. This approach eliminates the need for wide lenses, allowing the use of conventional-sized eyeglass lenses that maintain a normal appearance while still enabling reliable eye image capture.
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 a wider field of view, reduced bulkiness, and superior optical quality, allowing the device to be used like ordinary glasses with minimal distortion, enhancing usability and user experience.
Implementation Method 1
a first reflective surface inclined at a relatively small angle with respect to the eye's optical axis... certain embodiments use total internal reflection to accomplish at least one reflection within the light guiding prism
Implementation Method 2
a freeform corrective optical element... that together with the freeform prism, form an optical system that provides a distortion free viewing path for the subject
Data Source
AI summary
An optical system for eye tracking is disclosed. The system includes a light guiding prism that guides light from an ocular object to an imaging system through multiple internal reflections. The light guiding prism may include one or more freeform surfaces having optical power.