A control approach to cross coupling compensation of piezotube scanners in tapping-mode imaging

Abstract

In this article, an approach based on the recently-developed inversion-based iterative control (IIC) to cancel the cross-axis coupling effect of piezoelectric tube scanners (piezoscanners) in tapping mode atomic force microscope (AFM) imaging is proposed. Cross-axis coupling effect generally exists in piezoscanners used for 3D (x-y-z axes) nanopositioning in applications such as AFM, where the vertical z-axis movement can be generated by the lateral x-y axes scanning. Such x/y-to-z cross-coupling becomes pronounced when the scanning is at large range and/or at high-speed. In AFM applications, the coupling-caused position errors, when is large, can generate various adverse effects, including large imaging and topography distortions, and damage of the cantilever probe and/or the sample. This paper utilizes the IIC technique to obtain the control input to precisely track the couplingcaused x/y-to-z displacement (with sign-flipped). Then the obtained input is augmented as a feedforward control to the existing feedback control in tapping-mode imaging, resulting in the cancellation of the coupling effect. The proposed approach is illustrated through the exemplary applications of the nanoasperity measurement on harddisk drive. Experimental results show that the x/y-to-z coupling effect in large-range (20 μm) tapping-mode imaging at high scan rates (12.2 Hz to 24.4 Hz) can be effectively removed.