MEMS Mirror Spiral Scanning Frequency Tracking
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Solution Overview
Problem
Existing omnidirectional LiDAR devices with MEMS mirrors face challenges in maintaining a constant response phase during high-speed spiral rotation operations due to variations in resonance frequencies caused by process variations, temperature changes, and non-linear mechanical properties, making it difficult to achieve a linear change in the radius vector at high swing amplitudes.
Innovation Solution
An optical scanning device with a mirror portion that can swing around two orthogonal axes, driven by cyclic voltage signals with changing amplitudes and phases, ensuring the swing amplitudes around both axes change linearly, even when resonance and driving frequencies do not match, allowing for a fast and linear change in the radius vector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the amplitude of the driving signal is changed to increase or decrease the swing amplitudes of the MEMS mirror, then the spiral rotation operation can be performed, but the response phase cannot be kept constant when resonance frequency and driving frequency do not match, making linear radius vector change difficult to realize at high swing amplitudes
Solution Approach 1:
The patent changes the driving frequency to match the resonance frequency of the MEMS mirror. By dynamically adjusting the driving frequency parameter to coincide with the resonance frequency, the system maintains a constant response phase relationship between the driving signal and the mirror's swing motion, enabling linear radius vector change even at high swing amplitudes and fast change speeds of 0.5 rad/s or more
2Productivity
If the swing amplitude change speed is increased to achieve wider scanning range and higher frame rate, then productivity is improved, but the mismatch between resonance frequency and driving frequency becomes more significant, causing non-linear scanning
Solution Approach 1:
The patent dynamically adjusts the driving frequency parameter to track and match the resonance frequency of the MEMS mirror during operation. This frequency matching approach maintains the linear relationship between driving signal and mirror response even at high swing amplitude change speeds, enabling frame rates of 10 Hz or more while preserving the linearity of the scanning radius vector
3Device complexity
If the driving frequency is fixed and does not match the resonance frequency, then device complexity is reduced, but the spiral rotation operation cannot maintain linear radius vector change at high swing amplitudes
Solution Approach 1:
The patent implements dynamic frequency adjustment by changing the driving frequency to match the resonance frequency of the MEMS mirror. This parameter change approach maintains the linear radius vector change characteristic of spiral rotation operation at high swing amplitudes while keeping the control system relatively simple, avoiding the need for complex feedback control mechanisms
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 solution enables the realization of a spiral rotation operation with a high change speed of the swing amplitude, achieving a wide field of view and high frame rates in LiDAR applications, even under conditions where resonance and driving frequencies do not match, thereby overcoming the limitations of existing technologies.
Implementation Method 1
a first piezoelectric element surrounding the mirror portion in the first axis direction and configured to swing the mirror portion around the first axis; a second piezoelectric element surrounding the mirror portion in the second axis direction and configured to swing the mirror portion around the second axis
Implementation Method 2
In a case where a resonance frequency and a driving frequency around each of the first axis and the second axis all match, or in a case where the change speed of the swing amplitude is slow, the spiral rotation operation in which the radius vector changes linearly can be performed by changing only the amplitude of the driving signal
Data Source
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AI summary
Provided are an optical scanning device and a control method thereof capable of realizing a spiral rotation operation in which a change speed of a swing amplitude is fast and a radius vector changes linearly even in a case where a resonance frequency and a driving frequency do not match. An optical scanning device includes a mirror device that has a mirror portion, which is swingable around a first axis and a second axis orthogonal to each other, having a reflecting surface reflecting incident light, a first actuator causing the mirror portion to swing around the 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 the second axis by applying a rotational torque around the second axis to the mirror portion, and a processor that provides a first driving signal to the first actuator and provides a second driving signal to the second actuator. The processor, with the first driving signal and the second driving signal each as cyclic voltage signals whose amplitudes and phases change with time, causes the mirror portion to perform a spiral rotation operation including a period in which a swing amplitude around the first axis and a swing amplitude around the second axis change linearly.