Head-Mounted Display Alignment Assessment Using Strain Gauges
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Solution Overview
Problem
Head-mounted display systems experience misalignment issues due to flexing or bending, leading to inconsistent display imagery and user discomfort, which existing alignment assessment methods, such as those using large optical combiners, are costly and complex.
Innovation Solution
Incorporation of strain gauges, specifically Bragg gratings on optical elements, to detect misalignment by measuring strain-induced changes in light return parameters, allowing for real-time adjustment of display imagery to maintain alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large optical combiners are used for alignment assessment, then alignment measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the alignment assessment function from complex optical combiners and implements it using simple strain gauges attached to the frame. The strain gauges directly measure frame deformation without requiring additional optical components, thereby reducing device complexity while maintaining measurement capability.
Solution Approach 2:
Instead of using physical optical combiners to assess alignment, the patent creates a simplified model by measuring frame strain directly. The strain gauge readings serve as a proxy for alignment status, eliminating the need for complex optical paths while providing sufficient measurement precision for calibration purposes.
2Measurement precision
If optical combiners are used for alignment assessment, then alignment measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive, complex optical combiners with inexpensive strain gauges that can be easily manufactured and attached to the frame. The strain gauges provide adequate measurement precision at a fraction of the cost of optical combiners, making the system more economically viable.
Solution Approach 2:
The patent substitutes the mechanical/optical system (combiners) with an electrical sensing system (strain gauges). This replacement simplifies manufacturing while maintaining the ability to assess alignment through electrical resistance changes in the strain gauges rather than complex optical paths.
3Device complexity
If strain gauges are used for alignment assessment, then device complexity is reduced, but measurement precision may deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where strain gauge readings are continuously monitored and used to assess frame alignment. The system compares measured strain against calibration data to determine alignment status, providing sufficient precision through intelligent processing of simple sensor data rather than relying on complex hardware.
Solution Approach 2:
The patent changes the measurement parameter from direct optical alignment measurement to indirect strain measurement. By measuring frame deformation through strain gauge resistance changes and correlating this to alignment status, the system achieves adequate precision while using simple, low-complexity sensors.
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
Simpler, cost-effective alignment assessment that maintains display clarity and user comfort by dynamically adjusting imagery based on detected misalignments without the need for conspicuous optical combiners.
Implementation Method 1
a Bragg grating formed on an optical element of the wearable frame assembly. The Bragg grating includes a series of grating elements having a spacing between adjacent grating elements that corresponds to a wavelength of test light returned by the Bragg grating
Implementation Method 2
A head-mounted display system includes a wearable frame assembly, a display assembly mounted to the wearable frame assembly, a camera mounted to the wearable frame assembly, a test light source configured to output test light into an optical element configured to propagate the test light via total internal reflection
Data Source
AI summary
A head-mounted display system includes a wearable frame assembly and a display assembly mounted to the wearable frame assembly and configured to provide display light for viewing by a user eye. A camera mounted to the wearable frame assembly is configured to image a surrounding real-world environment. One or more strain gauges each have one or more variable strain parameters based at least in part on an amount of strain applied to the head-mounted display system. A logic machine is configured to assess an alignment of one or both of the display assembly and the camera based at least in part on the one or more strain parameters for each strain gauge of the one or more strain gauges.