Capacitive Charge Self-Sensing for MEMS Mirror Position
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Solution Overview
Problem
Microelectromechanical system (MEMS) mirrors in LIDAR systems face errors due to non-linear frequency response and external disturbances, leading to inaccuracies in mirror position measurement, which affects the precision of laser pointing and image resolution, especially in harsh environments.
Innovation Solution
An electrostatic oscillator system with a capacitive actuator and sensing circuit that measures deflection using displacement currents from multiple capacitive elements, allowing for precise control and compensation of systematic and non-systematic errors through a measurement circuit that integrates and matches current curves to calibration data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a MEMS mirror operates at resonance frequency to enable scanning, then scanning speed and productivity are improved, but non-linear frequency response and sensitivity to external disturbances cause position measurement errors and reduced reliability
Solution Approach 1:
The patent implements a feedback mechanism by continuously measuring the actual mirror position using capacitive sensing circuits and comparing it with the expected position. The system then compensates for deviations by adjusting the driving signal, thereby maintaining accurate position control despite non-linear frequency response and external disturbances during resonant operation
Solution Approach 2:
The patent replaces direct mechanical position measurement methods with capacitive sensing that measures electrical parameters (capacitance changes) to infer mirror position. This substitution allows for non-contact, high-precision measurement that is less susceptible to mechanical disturbances and can operate effectively during resonant scanning
2Adaptability or versatility
If the oscillator is influenced by external disturbances in harsh environments, then the system becomes more robust to real-world conditions, but the oscillation amplitude and frequency change due to non-linear dependency, causing laser pointing errors
Solution Approach 1:
The capacitive sensing circuit provides continuous feedback on the actual mirror position, enabling the control system to detect and compensate for position deviations caused by external disturbances such as temperature changes, pressure variations, and vibrations, thereby maintaining measurement precision despite environmental harshness
Solution Approach 2:
The capacitive elements serve dual functions: they act as actuators to drive the mirror oscillation and simultaneously serve as sensors to measure the mirror position. This multi-functionality allows the same structure to be used for both actuation and sensing, providing inherent compensation capabilities without requiring separate sensing mechanisms
3Measurement precision
If capacitive sensing is used to measure mirror position, then measurement precision is improved, but the system complexity increases due to additional sensing circuits and calibration requirements
Solution Approach 1:
The patent uses the same capacitive elements that form the actuator structure to also serve as position sensors. By measuring the capacitance changes of these existing elements, the system achieves precise position sensing without requiring completely separate sensing components, thereby reducing overall system complexity
Solution Approach 2:
The patent merges the actuation and sensing functions into a single integrated system. The capacitive elements are used both to drive the mirror oscillation and to sense the mirror position, combining what would traditionally be separate subsystems into one unified structure that reduces component count and simplifies the overall system
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 enhances the accuracy of MEMS mirror position sensing and control, improving the precision of LIDAR systems by compensating for errors and maintaining high image resolution even in harsh conditions.
Implementation Method 1
the actuator including a first capacitive element have a first capacitance dependent on the deflection and a second capacitive element having a second capacitance dependent on the deflection
Implementation Method 2
a sensing circuit configured to receive a first displacement current from the first capacitive element and a second displacement current from the second capacitive element
Implementation Method 3
integrate the first displacement current to generate a first capacitive charge value, and integrate the second displacement current to generate a second capacitive charge value
Implementation Method 4
an actuator configured to drive the electrostatic oscillator structure about the axis based on a driving signal
Data Source
AI summary
An oscillator system includes an electrostatic oscillator structure configured to oscillate about an axis based on a deflection that varies over time; an actuator configured to drive the electrostatic oscillator structure about the axis, the actuator including a first capacitive element having a first capacitance dependent on the deflection and a second capacitive element having a second capacitance dependent on the deflection; a sensing circuit configured to receive a first displacement current from the first capacitive element and a second displacement current from the second capacitive element, to integrate the first displacement current to generate a first capacitive charge value, and to integrate the second displacement current to generate a second capacitive charge value; and a measurement circuit configured to receive the first and the second capacitive charge values and to measure the deflection of the electrostatic oscillator structure based on the first and the second capacitive charge values.