Beyond Pull-in Stabilization of a 2-DOF Torsional Micro-Actuator using a Fuzzy Controller

Torsional micro-actuators have found variety of applications in optical switches, displays, interferometry, spectroscopy, abbreviation correction and biomedical imaging. In order to improve the performance of these systems, it is usually desirable to maximize their operating angle amplitude and their switching frequency. To reach this, the overshoot and the settling time of the system in following desired outputs should be minimized. The objective of this paper is to propose an optimal fuzzy controller to stabilize the angle of a torsion micro-actuator beyond its pull-in range. To do so, a dynamic model considering both rotational and translational degrees of freedom is considered. Using Lagrange equations, the differential equations of motion are derived. In the next step, the static behavior of the system is briefly reviewed. Also the effects of applied voltage and damping coefficient on both degrees of freedom are studied briefly. Based on the resulting understanding from the system, the required linguistic IF-THEN rules are derived. Using the famous combination of singleton fuzzifier, product inference engine and center average defuzzifier along with the fuzzy IF-THEN rules as the heart of the fuzzy system, a fuzzy controller is designed and simulated. The results show that the use of the designed controller and the closed-loop system can perfectly follow the commands either within or beyond the pull-in range with an acceptable overshoot and small settling time. It is expected that the designed controller be successfully utilized in analysis and optimization of torsional micro-actuators for better dynamic performance.