Contact-mode AFM control with modified surface topography learning observer and PTC

Atomic force microscope (AFM) is the instrument that can measure the surface of samples on the nano-scale. Most of the controllers of commercial AFMs are designed by classic control theory. However, sophisticated control theory has been applied in recent academic papers. Authors have already proposed a surface topography learning observer (STLO) based on disturbance observer theory. However, this method is not applicable to discrete-time non-minimum phase plant. In this paper, a modified surface topography learning observer is proposed based on zero-phase error inverse (ZPEI). Moreover, perfect tracking control (PTC) is utilized with scanned signal on previous-line. This approach can guarantee that the nominal error between surface topography and control input becomes perfectly zero at every sampling point if the topography of previous-line coincides with next-line. Experiments are carried out to show that the proposed methods achieve high-speed scanning only by the control algorithm without change of hardware.