A current cycle feedback iterative learning control approach to AFM imaging
In this article, we proposed a novel current cycle feedback (CCF) iterative learning control (ILC) approach to achieve high-speed imaging on atomic force microscope (AFM). AFM-imaging requires precision positioning of the AFM probe relative to the sample in 3-D (x-y-z) dimension. It has been demonstrated that with advanced control techniques such as the inversion-based iterative-control (IIC) technique, precision positioning of the AFM probe in the lateral (x-y) direction can be successfully achieved. Additional challenges, however, must be overcome to achieve precision positioning of the AFM-probe in the vertical direction. The main contribution of this article is the development of the CCF-ILC approach to the AFM z-axis control. Particularly, the proposed CCF-ILC controller design utilizes the developed robust-inversion technique to minimize the model uncertainty effect on the feedforward control, and remove the causality constraints existing in other CCF-ILC approaches. Experimental results for AFM imaging are presented and discussed to illustrate the proposed method.