Self-Locking Avoidance and Stiffness Compensation of a Three-Axis Micromachined Electrostatically Suspended...

Area of Science:

• * MEMS (Micro-Electro-Mechanical Systems) technology
• * Inertial sensing and accelerometry
• * Control systems engineering

Background:

• * Micromachined electrostatically-suspended accelerometers (MESA) offer potential for land seismic acquisition due to broad bandwidth, high sensitivity, and wide dynamic range.
• * Initial levitation of the proof mass (PM) in six degrees of freedom (DoFs) is challenging due to self-locking zones caused by cross-axis coupling effects in electrostatic suspension.
• * The inherent negative stiffness effect in electrostatic suspension limits amplitude-frequency response and suspension stiffness.

Purpose of the Study:

• * To propose an effective control scheme to overcome the initial levitation problem in MESA.
• * To minimize cross-axis coupling effects during electrostatic suspension.
• * To improve the broadband linear amplitude-frequency response and suspension stiffness of MESA for seismic applications.

Main Methods:

• * Analysis of coupling electrostatic forces and torques between lateral axes to identify self-locking zones.
• * Implementation of a control scheme involving delayed operation of a lateral actuator to solve initial levitation.
• * Application of a feed-forward compensation approach to mitigate the negative stiffness effect.

Main Results:

• * The proposed control scheme successfully achieved six-DoF suspension levitation of the PM from any initial position.
• * Feed-forward compensation resulted in a more broadband linear amplitude-frequency response and higher suspension stiffness.
• * Preliminary tests showed potential for MESA as a three-component MEMS geophone, with vacuum packaging identified as crucial for bandwidth extension and noise reduction.

Conclusions:

• * The developed control strategy effectively resolves the initial levitation challenge in MESA, enabling reliable six-DoF suspension.
• * The feed-forward compensation significantly enhances the dynamic performance, crucial for high-fidelity seismic measurements.
• * Vacuum packaging is essential for optimizing MESA performance, particularly for low-noise seismic data acquisition.