System Identification and Creep Compensation of Nanopositioning System Using Proportional and Double Integral Action

Abstract: Nanotechnology is precision control and manipulation of devices and materials at nanoscale i.e. nanopositioning. Nanopositioners are precision mechatronics system designed to move objects over a small range with a resolution down to a fraction of an atomic diameter. In particular, desired specifications of nanopositioners are fast response with no or very little overshoot, large travel range with very high resolution, extremely high precision and high bandwidth. This paper presents the identification of nanopositioning device consisting of flexure stage for motion of sample and piezoelectric crystal as both sensor and actuator. Open loop behaviour of the nanopositioning device on the basis of time and frequency responses is plotted and analysed. To improve the system characteristics feedback controllers are implemented and simulated. In this paper, PI and PII controllers are designed and system performances are investigated for different values of feedback gain. Step response and frequency response under variety of conditions are obtained to verify the effectiveness of these feedback controllers. A positioning system utilizing piezoelectric actuators typically exhibits creep, hysteresis and lightly damped vibration modes which limits the usable bandwidth. In this paper, in order to control the creep nonlinearity, different controllers are implemented. Then a comparative study of traditional P and PI controller with PII controller on the basis of time and frequency response is given to show which controller is better. Simulation results for the performance analysis are carried out in MATLAB.

Keywords: Nanotechnology, nanopositioning, piezoelectric actuators, feedback controller, PI controller, PII controller, Nonlinearities, Creep.