Design of electrostatic actuators for suppressing vertical disturbances of CMOS-MEMS capacitive force sensors in bio applications

Department of Mechatronics Engineering, Sharif University of Technology, International Campus, Amir Kabir Square, Kish, Iran

^a Corresponding author: r.jalilmozhdehi@sharif.kish.ac.ir

Received: 26 August 2014
Accepted: 23 December 2014

Abstract

The objective of this work is to design electrostatic actuators for a CMOS-MEMS nano-newton capacitive force sensor to suppress vertical vibrations disturbances. Electrostatic actuators are selected because the movable part of this force sensor is anchored to the fixed parts. In the first step, we propose a framework for simulation of the force sensor based on finite element method. The proposed model is modified utilizing comparison between the simulation and experimental models to improve the performance of the model. Then, 14 pairs of electrostatic actuators are designed for applying the control algorithm and their pull-in voltage is calculated. In next step, Modal Analysis is applied to find dominant natural frequencies and mode shape vectors. In addition, an observer is proposed to estimate the velocity of the modal coordinate. Finally, an optimal controller is designed employing state-space approach to suppress vertical vibration due to undesired out-of-plane excitations generated by environment during manipulation. Simulation results illustrate that employing optimum LQR control approach, the maximum out-of-plane disturbance input is suppressed less than 0.4 s with acceptable range of voltage less than pull-in voltage.