HMD Active Optics Feedback for Lens Calibration Drift
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Solution Overview
Problem
Conventional head-mounted display (HMD) optical systems face calibration issues due to changes in atmospheric pressure and other conditions, leading to inaccuracies in adjustable lens actuation, causing visual fatigue and nausea if vergence and accommodation conflicts are not correctly managed.
Innovation Solution
An optical system with dynamically-generated feedback for the adjustable lens, using an illumination layer with point light sources and an active optics block that includes an adjustable lens controller and actuators, processes calibration images to adjust actuation and maintain desired optical power, compensating for distortions caused by environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional HMD optical systems are used without active feedback, then the device complexity is low, but the manufacturing precision and reliability deteriorate due to calibration drift from atmospheric pressure changes and actuator sag
Solution Approach 1:
The patent implements an active feedback control system where a camera captures images of calibration targets, the image processor determines lens distortion, and the controller adjusts actuator signals in real-time to compensate for calibration drift. This closed-loop feedback mechanism maintains manufacturing precision despite environmental changes and component aging.
Solution Approach 2:
The system performs self-calibration by using the device's own camera and processing capabilities to detect and correct its own optical distortions. The calibration process is automated, requiring no external equipment or manual intervention, allowing the system to self-correct for atmospheric pressure changes and actuator sag.
2Reliability
If dynamic feedback calibration is implemented, then the reliability improves under varying conditions, but the device complexity and energy consumption increase
Solution Approach 1:
The system performs calibration at periodic intervals rather than continuously, triggering calibration sequences based on elapsed time, altitude changes, or user interaction. This periodic approach maintains reliability by correcting drift when needed while minimizing energy consumption by keeping the calibration system dormant during normal operation.
Solution Approach 2:
The system performs preliminary calibration during manufacturing and initialization, establishing baseline parameters before normal operation. This preliminary calibration reduces the frequency and intensity of subsequent calibration events, lowering energy consumption while maintaining reliability through targeted corrections.
3Manufacturing precision
If calibration is performed frequently to maintain accuracy, then the manufacturing precision is maintained, but the loss of time increases due to calibration interruptions
Solution Approach 1:
The system implements rapid calibration sequences that complete distortion correction in minimal time, using optimized algorithms and hardware acceleration in the image processor. Calibration is rushed through efficiently by leveraging pre-computed lookup tables and streamlined measurement protocols, maintaining precision while minimizing user-perceived interruption time.
Solution Approach 2:
Calibration data and correction parameters are pre-computed and stored during manufacturing and initial setup. During operation, the system applies pre-prepared correction tables rather than performing full calibration sequences, maintaining manufacturing precision while eliminating time-consuming real-time computation and user interruption.
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
Ensures accurate and real-time adjustment of the adjustable lens, reducing visual fatigue and nausea by maintaining correct focus and alignment, even under varying conditions such as altitude changes or actuator sag.
Implementation Method 1
an adjustable lens configured to modify an optical power of display light generated by the display layer for presentation to a user of the HMD
Implementation Method 2
a camera configured to generate a calibration image in response to calibration light emitted by the array of point light sources
Implementation Method 3
an adjustable lens controller configured to process the calibration image to determine a distortion in the array of points included in the calibration image
Data Source
AI summary
An optical system for a head mounted display (HMD) includes a display layer, an illumination layer, an optical combiner, and an active optics block. The display layer is configured to emit display light and the illumination layer includes an array of point light sources configured to emit calibration light. The optical combiner is configured to pass the display light to a front side of the optical system and to direct the calibration light to a camera. The active optics block includes an adjustable lens disposed between the illumination layer and the optical combiner, where the adjustable lens is configured to pass the calibration light to the optical combiner and to focus the display light for a user of the HMD. The active optics block is further configured to adjust an optical power of the adjustable lens based on a calibration image captured by the camera responsive to the calibration light.