Modeling And Control Of Piezoelectric Actuator Of Atomic Force Microscope

With human beings exploring the micro world, micro/nanopositioning technology has been developed quickly in the past years. As a system with the ability of atomic resolution, atomic force microscope (AFM) is widely used in micro-positioning and manipulating. At present, many commercial AFMs use piezoelectric ceramic as their 3-degree of freedom micro-positioning actuators. However, the inherent properties of piezoelectric ceramic, such as hysteresis nonlinearity and vibration, limit the scanning speed of AFM. As a result of that, AFM could not satisfy the request of real-time observing or manipulation of dynamic samples, and is restricted in real-time application. For these reasons, this t(?)esis aims at speeding the scanning without lowering the accuracy of AFM imaging from the view of system and control point.The work is based on the Scientific and Technological Project of Shandong Province:"Key Technology of Reliable Intelligent Atomic Imaging and Manipulating for Micro-system". The main contents are as following:â… . Property Analysis of Piezoelectric ActuatorsPiezoelectric materials'expansion mechanism is analyzed. Based on the study of piezoelectric effect and converse piezoelectric effect, several inherent chara cteristics of piezoelectric stack actuators, such as creep, hysteresis, vibration, are described, mainly with respect to their restrictions to accurate micro-positioning.â…¡. Compensation of Hysteresis NonlinearityTo investigate the compensation of hysteresis, the classical PI modeling approach is considered and several drawbacks of this model are figured out. Furthermore, a modified PI model is established. And then, a feedforward controller which is based on the modified PI model is designed and is used for the compensation strategy.â…¢. Compensation of VibrationA second-order linear dynamic model of micro-positioning system is built and three kinds of damping controllers, such as polynomial-based pole placement controller, positive position feedback controller, are designed to damp the first resonant mode of piezoelectric actuator, aiming at attenuating the effect of vibration.â…£. Control of High-speed Micro-positioning SystemThe hysteresis compensator and damping controller are combined for the integrated control of the piezoelectric actuator. Based on the integrate control strategy, high-speed and large-range scanning control of micro-positioning system is achieved, and the conclusion could be verified by the simulation results.At the last part of the thesis, the main contents are summarized and suggestions of the future research work in this field are given.