MEMS Mirror Overtone Mode Control for LiDAR Line Spacing
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Solution Overview
Problem
Existing optical scanning devices using MEMS mirrors for spiral rotation in LiDAR systems face challenges in maintaining consistent line spacing, leading to variations in resolution, especially when driven in resonance modes.
Innovation Solution
The optical scanning device employs a mirror device with actuators that apply rotational torques around orthogonal axes, and a processor that generates cyclic voltage signals for the actuators. The device is designed to operate within specific resonance modes, with frequency filter processing to ensure a voltage level ratio of −55 dBV or less, thereby reducing line spacing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the MEMS mirror is driven by using a resonance mode in which the actuator and the mirror portion swing in a relationship of opposite phases, then driving efficiency is improved, but line spacing variation becomes remarkable
Solution Approach 1:
The patent changes the driving frequency parameter from a basic resonance mode to an overtone mode (higher-order resonance mode). This parameter change allows the system to maintain resonance-driven efficiency while achieving more uniform line spacing in the spiral orbit, as the overtone mode produces a different vibration pattern that reduces the harmful non-uniformity effects
Solution Approach 2:
The patent dynamically adjusts the driving approach by selecting specific resonance modes (overtone modes) rather than using a fixed basic resonance mode. This dynamic selection of operating modes allows the system to optimize both driving efficiency and line spacing uniformity based on the desired performance characteristics
2Area of moving object
If the amplitude of the sinusoidal driving signal is increased to increase the swing amplitude of the mirror portion, then the scanning range is improved, but the line spacing variation in the spiral orbit becomes more significant
Solution Approach 1:
The patent changes the resonance mode parameter from basic mode to overtone mode, which fundamentally alters how the mirror responds to driving signals. This parameter change allows for larger swing amplitudes (wider scanning range) while maintaining better line spacing uniformity, as the overtone mode's vibration characteristics are less sensitive to amplitude variations
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 approach effectively reduces line spacing variations in the spiral orbit, enhancing the resolution and frame rate of the LiDAR system without compromising the efficiency of the MEMS mirror operation.
Implementation Method 1
a first actuator causing the mirror portion to swing around a first axis by applying a rotational torque around the first axis to the mirror portion, and a second actuator causing the mirror portion to swing around a second axis by applying a rotational torque around the second axis to the mirror portion
Implementation Method 2
A resonance mode of one lower order than a basic resonance mode closest to a frequency of the cyclic voltage signal exists in at least any one of a plurality of resonance modes accompanied by a mirror tilt swing around the first axis or a plurality of resonance modes accompanied by the mirror tilt swing around the second axis
Implementation Method 3
having a reflecting surface reflecting incident light
Data Source
AI summary
A resonance mode of one lower order than a basic resonance mode closest to a frequency of a cyclic voltage signal exists in at least any one of a plurality of resonance modes accompanied by a mirror tilt swing around a first axis or a plurality of resonance modes accompanied by the mirror tilt swing around a second axis. In a case where a resonance frequency of one higher order from a frequency of the basic resonance mode is frH, a ratio of a first voltage level to a second voltage level which is a maximum voltage level value in the entire frequency range among frequency components of the cyclic voltage signal is satisfied to be −55 dBV or less, where a maximum voltage level value in a frequency range of (1± 1/20)×frL and a frequency range of (1± 1/20)×frH among the frequency components of the cyclic voltage signal is the first voltage level for an axis in which the lower-order resonance mode exists among the first axis and the second axis, and a maximum voltage level value in the frequency range of (1± 1/20)×CrH among the frequency components of the cyclic voltage signal is the first voltage level for an axis in which the lower-order resonance mode does not exist among the axes.