A robust control approach for MEMS capacitive micromachined ultrasonic transducer

Abstract

An optimal composite nonlinear feedback control method with integral sliding mode is presented in this paper. The controller extends the travel range of the micro-electromechanical system capacitive micromachined ultrasonic transducer (CMUT). Moreover, enhanced transient response and precise tracking performance is achieved. It is known that CMUT is inherently unstable which results in pull-in phenomenon and it is very sensitive to small perturbations, so one of the major problems is to stabilize the CMUT beyond the pull-in limit with the external disturbances. In addition, the input saturation problem is significant to CMUT. Based on that, a robust control scheme is derived using composite nonlinear feedback control law combined with integral sliding mode control law. Then all the tuning parameters for the proposed control method are converted into a minimization problem and solved by particle swarm optimization algorithm automatically. We verified the effectiveness through extending the travel range of the CMUT gap by three control methods which are proportional integral derivative, composite nonlinear feedback and the method we proposed. The stability and small range tracking performance with three control methods is compared on the pull-in position of CMUT. The simulations show that the proposed control method has desired tracking performance and robustness to external disturbance with input saturation.