HMD Fiducial Filtering for Precise Display Alignment
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Solution Overview
Problem
HMD devices face misalignment issues between left and right eye images due to temperature changes and drift, causing dipvergence, which are exacerbated by non-rigid frames, and current DAT systems suffer from signal-to-noise ratio (SNR) issues and light loss through prisms, leading to visual disruption.
Innovation Solution
Implement a visible light filter along the DAT optical path to perform color-specific blanking of fiducial images, using a controller to output a fiducial image with a specific color of light transmitted by the filter, and optionally using separate fiducial image projectors to reduce visual distraction while maintaining SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DAT system is implemented to monitor alignment of left and right eye images, then alignment precision is improved, but visual disruption to the user increases due to fiducial images being visible
Solution Approach 1:
The patent applies local quality by making the fiducial image visible only in specific local regions (fiducial portions) of the display, while the rest of the display content remains normally visible. This is achieved by projecting fiducial images at different intensities in different regions, allowing alignment monitoring without overall visual disruption.
Solution Approach 2:
The patent uses color changes by projecting fiducial images in different color intensities or wavelengths than the main display content. The fiducial images can be projected in a color range that is less distracting to users while still being detectable by the camera system for alignment monitoring.
2Measurement precision
If fiducial images are projected for alignment tracking, then alignment monitoring capability is improved, but signal-to-noise ratio deteriorates due to light loss through optical components
Solution Approach 1:
The patent extracts the fiducial image projection function from the main display system by using separate projection capabilities. This allows the fiducial images to be projected independently with optimized optical paths that minimize light loss, while the main display content continues uninterrupted.
Solution Approach 2:
The patent employs composite optical paths that combine different optical components (mirrors, beam splitters, filters) to efficiently transmit fiducial image light while minimizing losses. The optical system is designed as a composite structure that preserves signal strength for alignment tracking.
3Adaptability or versatility
If separate left and right display image projectors are used to generate stereoscopic images, then image generation capability is improved, but alignment stability deteriorates due to temperature changes and drift
Solution Approach 1:
The patent implements feedback by using the DAT system to continuously monitor the alignment of fiducial images from both projectors. The camera detects fiducial image positions, and this information is fed back to the controller, which automatically adjusts the projectors to maintain proper alignment despite temperature changes or drift.
Solution Approach 2:
The patent applies preliminary action by projecting fiducial images along with the main display content from the beginning. This allows the system to proactively monitor and correct alignment issues before they affect the user experience, rather than reacting to misalignment after it occurs.
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
Maintains desired SNR for fiducial image detection while reducing visual disruption to the user, allowing for effective alignment adjustment of left and right eye images.
Implementation Method 1
a visible light filter located along the DAT optical path
Implementation Method 2
a camera optically coupled to an output of the DAT optical path
Data Source
AI summary
One example provides a head mounted display (HMD) device comprising a projection system and left eye and right eye display optical paths configured to transmit left eye and right eye images for viewing. The projection system comprises left and right display image projectors. The HMD device further comprises a display alignment tracker (DAT) system comprising a DAT optical path comprising left side and right side DAT optical paths. The DAT system further comprises a camera coupled to an output of the DAT optical path, and a visible light filter located along the DAT optical path. The HMD device further comprises a controller configured to control the projection system to output a fiducial image comprising a visible color of light transmitted by the visible light filter and to blank the visible color of the fiducial image from a fiducial portion of both the left and right eye images.