MEMS Micromirror Position Control With Resonance Equalization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing open loop driving techniques for quasi static MEMS mirrors in laser beam scanning modules are limited in accurately positioning the mirrors due to mechanical resonance and external vibrations, and cannot extend system bandwidth beyond 2kHz while maintaining mechanical opening angles, leading to spurious ringing and disturbances in the mirror's travel path.
Innovation Solution
A control system with a compensator-based controller and derivative-based controller is implemented, which includes a higher order resonance equalization circuit and lead-lag filters to dampen the fundamental resonant mode and extend system bandwidth by generating feedback signals that correct positional errors and minimize ringing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If open loop driving techniques are used for quasi static MEMS mirrors, then the system bandwidth can be extended beyond 2kHz, but mechanical resonance generates spurious ringing and positional errors that cannot be accurately corrected
Solution Approach 1:
The patent implements a closed-loop control system that uses a position sensor to continuously monitor the actual mirror position and feeds this information back to a controller. The controller compares the actual position with the desired position and generates corrective drive signals to eliminate positional errors and ringing caused by mechanical resonance, thereby maintaining high bandwidth while achieving accurate positioning.
Solution Approach 2:
The patent replaces open-loop mechanical driving with a closed-loop electromechanical control system. Instead of relying solely on mechanical resonance characteristics, the system uses electronic feedback control to actively compensate for resonance effects, substituting passive mechanical behavior with active electronic correction to achieve both high bandwidth and positioning accuracy.
2Speed
If drive signals with fast slopes are used to achieve high bandwidth, then system response speed improves, but mechanical resonance is excited causing ringing and disturbances in mirror travel path
Solution Approach 1:
The closed-loop system detects ringing and disturbances through position sensing and generates real-time feedback signals to counteract these harmful oscillations. The controller actively suppresses resonance by applying corrective forces opposite to the detected vibrations, allowing fast drive signals to be used without generating harmful ringing.
Solution Approach 2:
The patent converts the harmful effect of mechanical resonance into a beneficial one by using the resonance information from position sensing to generate proactive compensation signals. The system detects resonance patterns and uses this information to pre-compensate or actively cancel the ringing, transforming the harmful resonance into a detectable and correctable phenomenon that improves overall system performance.
3Reliability
If external vibrations are introduced into linearly driven MEMS mirrors, then positioning accuracy deteriorates, but open loop techniques cannot compensate for these vibrations
Solution Approach 1:
The closed-loop control system uses position sensing to detect vibrations caused by external disturbances and generates real-time feedback compensation signals. The controller continuously adjusts the drive signal based on detected positional deviations, actively counteracting external vibrations and maintaining stable positioning despite environmental disturbances.
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 control system effectively dampens the quality factor of the fundamental resonant mode, reduces positional errors, and extends the system bandwidth, allowing for precise control of MEMS mirrors even at frequencies close to mechanical resonance, thereby improving the accuracy and stability of the mirror's movement.
Implementation Method 1
a piezoelectric actuator adapted to rock the mirror around an axis of the mirror
Implementation Method 2
a piezoelectric sensor adapted to sense vibrations of the piezoelectric actuator
Implementation Method 3
the relatively large quality factor (e.g., 100) and low frequency (about 500-1000 Hz) of the fundamental resonant mode of quasi statically driven MEMS micromirrors
Implementation Method 4
it is clear that further development into the driving of quasi static MEMS micromirrors is necessary, for example to dampen fundamental resonant modes
Data Source
Figure 1~2B
Figure 3A~4
Figure 5~7
AI summary
Disclosed herein is a control system (10) for a projection system (17), including a first subtractor (12) receiving an input drive signal (INPUT) and a feedback signal (FBK) and generating a first difference signal (DIFF1) therefrom, the feedback signal being indicative of position of a quasi-static micromirror (19b) of the projection system. A type-2 compensator (15a) receives the first difference signal (DIFF1) and generates therefrom a first output signal (OUT1). A derivative based controller (15b) receives the feedback signal (FBK) and generates therefrom a second output signal (OUT2) . A second subtractor (16) receives the first (OUT1) and second (OUT2) output signals and generates a second difference signal (DIFF2) therefrom. The second difference signal serves to control a mirror driver (19a) of the projection system. A higher order resonance equalization circuit (20) receives a pre-output signal from an analog front end (19c) of the projection system that is indicative of position of the quasi-static micromirror (19b), and generates the feedback signal (FBK) therefrom.