A 2DOF control of an AFM system based on an improved P-I model

For the sake of the hysteresis characteristics and dynamic behavior description of the piezo-scanner, an improved Prandtl-Ishlinskii(P-I) hysteresis model for an Atomic Force Microscope (AFM) system in X-axis is established, which is then utilized to design a 2DOF tracking controller combined feedforward control with feedback control, achieving accurate tracking performance for an given trajectory in AFM horizontal direction. Specifically, considering the piezo-scanner features, a cascade model based on advanced P-I hysteresis model is designed utilizing N4SID algorithm, obtaining wider adaptability, higher accuracy. Furthermore, a 2DOF controller is designed to improve the system bandwidth and tracking accuracy, where an inverse model based on P-I hysteresis model is utilized as the feedforward controller which compensates the hysteresis characteristics, while a normal PI controller is used as the feedback controller to further improve the system tracking accuracy. The proposed modeling and control strategies are implemented and then applied to a practical AFM system, with the obtained experimental results clearly showing the superior tracking performance over other controllers including direct drive controller, PI feedback controller and P-I inverse feedforward controller.