大范围高速原子力显微镜的前馈反馈混合控制方法

摘要

In order to expand the application scope of Atomic Force Microscopes(AFMs), a largerange 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.%为了扩大原子力显微镜(Atomic Force Microscope,AFM)使用范围,研制了一套大范围高速AFM系统.针对大范围高速扫描时Z方向控制问题,提出了前馈反馈混合控制方法.前馈控制包括自动调平前馈和基于前一行扫描前馈,前者通过多线扫描确定样品倾斜位置,将所有扫描点的倾斜位移差用函数式表达,然后将其换算为Z向驱动电压后驱动下扫描器运动;后者利用前一行扫描高度数据作为当前行Z向扫描器驱动的参考输入.反馈控制为在普通比例-积分(PI)控制基础上改进的动态P参数PI控制,P参数设置与误差大小有关.实验结果表明:采用本控制方法最大控制误差由40.17 nm减小为6.01 nm,误差均方根值由22.85 nm减小为2.01 nm,明显抑制了误差信号,提高了Z向控制效果,获得了更精确的高度图像.