MEMS Mirror Quasi-Static Actuation via Electrostatic Drive
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Solution Overview
Problem
Existing two-axis MEMS mirrors face challenges in achieving high enough tilt amplitude about the quasi-static oscillation axis while maintaining low damping for high-frequency oscillations, which is difficult to control in low-pressure sealed cavities.
Innovation Solution
The MEMS mirror apparatus incorporates an electrostatic drive mechanism with an elongated drive plate, lever, and spring arrangement to facilitate a quasistatic see-saw motion of the reflector entity, allowing for accurate control of quasi-static oscillations even in low-pressure sealed cavities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the MEMS mirror is placed in a low-pressure sealed cavity to achieve low damping for high-frequency oscillations, then the high-frequency oscillation performance is improved, but the quasi-static oscillation becomes underdamped and hard to control
Solution Approach 1:
The patent divides the control system into two independent parts: a piezoelectric actuator for high-frequency oscillations and a separate electrostatic actuator for quasi-static oscillations. This segmentation allows each actuator to be optimized for its specific function without interfering with the other, resolving the control difficulty caused by the coupled system in low-pressure environments.
Solution Approach 2:
The patent introduces an electrostatic actuator as an intermediary mechanism that mediates between the control system and the reflector for quasi-static oscillations. This intermediary provides precise control capability in the low-pressure environment where direct control would be difficult, allowing independent adjustment of quasi-static oscillation parameters.
2Speed
If piezoelectric actuators are used to place the mirror into static tilted position during quasi-static actuation mode, then the actuation speed is improved, but hysteresis effects make precise positioning difficult
Solution Approach 1:
The patent replaces the piezoelectric actuator (which exhibits hysteresis) with an electrostatic actuator for quasi-static positioning. The electrostatic actuator uses electric field forces instead of piezoelectric deformation, eliminating hysteresis effects and enabling precise, repeatable positioning while maintaining fast response characteristics.
Solution Approach 2:
The patent changes the actuation mechanism from piezoelectric to electrostatic for quasi-static operations. This parameter change in the actuation method eliminates the hysteresis characteristic inherent in piezoelectric materials, allowing for precise control of the mirror's tilted position without the positioning errors caused by hysteresis.
3Stability of the object's composition
If the drive force is increased to prevent unwanted motions in quasi-static oscillation, then the control stability is improved, but vertical vibrations are induced in the loose moving structures
Solution Approach 1:
The patent applies different actuation characteristics to different operational modes: the electrostatic actuator provides high force and stability for quasi-static oscillation control, while the piezoelectric actuator handles high-frequency oscillations. This local optimization of actuator properties for specific functions allows stable control without inducing harmful vibrations in the loose moving structures.
Solution Approach 2:
The patent implements dynamic control by using two actuators with different characteristics for different oscillation modes. The electrostatic actuator dynamically adjusts quasi-static positions with high precision and stability, while the piezoelectric actuator dynamically responds to high-frequency signals. This dynamic allocation of control functions prevents unwanted vibrations while maintaining stability.
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 accurate and controlled quasi-static oscillations, overcoming the challenges of achieving high tilt amplitudes and maintaining low damping, thus improving the performance of MEMS mirrors in applications like LIDAR and augmented reality.
Implementation Method 1
The at least one first actuator is an electrostatic actuator comprising a moveable electrode plate formed by or attached to the respective elongated drive plate and a static electrode plate superposed with the moveable electrode plate above or below the frame plane
Implementation Method 2
at least one lever extending from the at least one elongated drive plate and at least one first spring coupling the at least one lever to the reflector entity or to an arm extending from the reflector entity
Data Source
Figure 1~2A
Figure 2B~2E
Figure 3~4B
AI summary
The disclosure relates to MEMS mirror apparatus and a method to drive a MEMS mirror apparatus. A reflector entity comprising a reflector (10), or a reflector (10) and a gimbal (15) is configured to be driven into a quasistatic see-saw motion about a quasi-static oscillation axis (100) by means of electrostatically driving at least one elongated drive plate (20a, 20b) into a first drive motion. The drive motion is conveyed to the reflector entity by means of at least one lever (22a, 22b) extending from the at least one elongated drive plate (20a, 20b) and at least one first spring (18a, 18b) coupling the at least one lever (22a, 22b) to the reflector entity or to an arm (19) extending from the reflector entity. The first drive motion is a quasi-static see-saw drive motion of the elongated drive plate (20a, 20b) about a drive axis (110a, 110b) aligned with longitudinal dimension of the elongated drive plate (20a, 20b).