Feed-forward and feed-back controller for large-range and high-speed AFM

In order to expand the application scope of Atomic Force Microscopes(AFMs),a large-range and high-speed AFM was developed.A feed-forward and feed-back algorithm is proposed to deal with the Z-control of the AFM.The feed-forward controller includes an auto leveling controller and a last line based controller.The former determines the location of sample tilt by multi-lines scan,and the tilt displacements of all scan points are expressed by a formula.Then,it is transformed into Z control voltages to drive the down-stage.The latter uses the last line height signal as the reference input of Z-control in the current line scan.The feed-back controller is a proportional integral(PI) controller whose P parameter is dynamically changed with error signals.Experimental results indicate that the max error value by proposed method is decreased from 40.17 nm to 6.01 nm,and the root-mean-square error is decreased from 22.85 nm to 2.01 nm.It suppresses error signals evidently,enhances the effectiveness of Z-control,and makes image more precise.