Lissajous Scanning Mirror Modulation for AR Display Resolution
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Solution Overview
Problem
Conventional Lissajous scanning in augmented reality displays suffers from uneven pixel resolution due to sinusoidal oscillations of the MEMS mirror, leading to high local density at the periphery and low local density in the middle of the image plane, limiting the display's pixel resolution and refresh rate.
Innovation Solution
A display apparatus with a mirror assembly oscillating about two axes, where the excitation signals are modulated based on the Region of Interest (ROS) to adjust the per-pixel refresh rate and number of light beam passes, allowing for increased pixel resolution and refresh rate by altering the Lissajous trajectory's local density, thereby optimizing the display for minimal flickering and high perceived resolution without increasing oscillation frequencies or frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Lissajous scanning is used with resonant oscillation about both axes, then higher frame rates and lower power consumption are achieved, but uneven pixel resolution occurs with high local density at periphery and low local density in middle
Solution Approach 1:
The patent applies local quality by modulating the excitation signals to create different trajectory densities in different regions of the image plane. Specifically, the modulation signals are designed to increase the local density of the Lissajous trajectory in the middle region (region of interest) while maintaining or reducing density at the periphery, thereby achieving uniform pixel resolution across the entire image plane while preserving the high frame rate benefits of resonant Lissajous scanning
2Area of stationary object
If the light beam scans the entire image plane uniformly, then complete image coverage is achieved, but the region of interest receives insufficient light beam passes resulting in low pixel resolution
Solution Approach 1:
The patent implements local quality by designing modulation signals that concentrate the light beam passes in the region of interest. The first and second modulation signals are specifically configured to increase the local density of the Lissajous trajectory within the region of interest, ensuring that this area receives sufficient light beam passes for high pixel resolution while the rest of the image plane maintains adequate coverage
Solution Approach 2:
The patent uses periodic modulation signals applied to the excitation signals of the MEMS mirror. These periodic modulations create a time-varying trajectory pattern where the light beam repeatedly passes through the region of interest at optimized intervals, ensuring consistent high-resolution rendering in this area across multiple image frames
3Manufacturing precision
If excitation signal frequencies are increased to improve resolution, then pixel resolution increases, but power consumption and actuator requirements increase
Solution Approach 1:
The patent applies parameter changes by modulating the excitation signals with specific modulation signals that alter the effective trajectory density without changing the fundamental oscillation frequencies. This allows the system to achieve higher pixel resolution in the region of interest by optimizing the time-spent-weighted pixel resolution through signal modulation rather than increasing the mechanical oscillation frequencies, thereby avoiding increased power consumption and actuator requirements
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
The solution achieves optimized pixel resolution and refresh rate within the ROS, ensuring a flicker-free AR display with high perceived quality, while maintaining low power consumption and small actuator requirements, and smoothly transitions between regions of high and low resolution.
Implementation Method 1
the mirror oscillates resonantly—or near resonance—about both axes
Implementation Method 2
In so-called Lissajous scanning the mirror oscillates resonantly—or near resonance—about both axes. The frequencies of oscillation about the two axes are greater than the frame rate and the beginnings of their respective oscillation periods usually meet only every one or more frames.
Data Source
AI summary
An apparatus for displaying a virtual scene comprises a display wearable on a user's head and a graphics controller configured to calculate, from scene data representing the virtual scene, image data for the display such that the virtual scene is displayed in the environment irrespective of the head's position and pointing direction, the virtual scene appearing in the image data in a region of scene, wherein the graphics controller is configured to modulate excitation signals of a Lissajous scanning mirror assembly, which diverts the light beam of a light source, by modulation signals which are dependent on the region of scene.