Scanning Mirror Assembly for Tiled HMD Resolution
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Solution Overview
Problem
Conventional MEMS scanners in head-mounted displays face a trade-off between mirror size and resonance frequency, limiting the number of scan lines that can be effectively scanned due to the diffraction spread angle and resonance frequency constraints, resulting in poor resolution for users.
Innovation Solution
A scanning mirror assembly with a range of scanning frequencies along both slow and fast axes, utilizing scanning mirrors with diameters between 1 to 3 mm, operates at frequencies of up to 40 kHz, allowing for improved resolution without compromising the trade-off between mirror size and scanning frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large mirror is used in MEMS scanner, then the diffraction spread angle is reduced improving resolution, but the resonance frequency decreases limiting the number of scan lines
Solution Approach 1:
The scanning system is divided into multiple independent MEMS scanners, each handling a portion of the overall scanning task. This segmentation allows each scanner to use smaller mirrors with higher resonance frequencies while collectively achieving the required resolution and scan line capacity through coordinated operation of multiple scanners.
2Speed
If a small mirror is used in MEMS scanner, then the resonance frequency is high enabling more scan lines, but the diffraction spread angle increases reducing resolution
Solution Approach 1:
Multiple MEMS scanners with small mirrors are combined to work together as a unified scanning system. The collective output of these scanners achieves the resolution equivalent to a single large mirror system while maintaining the high resonance frequency advantage of small mirrors, thus enabling more scan lines without sacrificing resolution.
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 configuration enhances the resolution of the output image displayed to the user's eye by optimizing the scanning frequencies and mirror size, enabling a higher number of scan lines while maintaining image quality.
Implementation Method 1
The scanning mirror assembly includes one or more scanning mirrors that resonate at a resonance frequency and that vibrate in response to actuation signals. The scanning mirrors operate within a first range of scanning frequencies along a slow axis and a second range of scanning frequencies along a fast axis.
Implementation Method 2
In the far-field, mirror size determines the diffraction spread angle of the scanned laser beam. A large mirror is used to have a smaller diffraction spread angle.
Implementation Method 3
The scanning mirrors resonate at a resonance frequency and that vibrate in response to actuation signals.
Data Source
AI summary
A head mounted display (HMD) system includes a light source, a scanning mirror assembly, and an output screen. The light source includes source elements that emit image light. The scanning mirror assembly scans the image light at least along one dimension to form tiled portions of scanned image light of an output image. The scanning mirror assembly directs at least one of the tiled portions of the output image to a first position, and redirects at least one of the tiled portions of the output image to a second position adjacent to the first position. The scanning mirror assembly includes scanning mirrors operating within a first range of scanning frequencies along a slow axis and a second range of scanning frequencies along a fast axis. The output screen outputs a tiled image light to an eyebox region using the scanned image light.