Robust Repetitive Controller for Fast AFM Imaging

TL;DR

This paper introduces a robust repetitive controller for AFM that leverages the repetitive nature of lateral movements to significantly improve scan speed and reduce interaction forces, outperforming conventional controllers.

Contribution

A novel repetitive controller design for AFM's z-axis that enhances scanning speed and reduces forces by utilizing previous scan profiles.

Findings

Scan error reduced by 66%

Average tapping forces reduced by 58%

Scan speed increased by 7 times

Abstract

Currently, Atomic Force Microscopy (AFM) is the most preferred Scanning Probe Microscopy (SPM) method due to its numerous advantages. However, increasing the scanning speed and reducing the interaction forces between the probe's tip and the sample surface are still the two main challenges in AFM. To meet these challenges, we take advantage of the fact that the lateral movements performed during an AFM scan is a repetitive motion and propose a Repetitive Controller (RC) for the z-axis movements of the piezo-scanner. The RC utilizes the profile of the previous scan line while scanning the current line to achieve a better scan performance. The results of the scanning experiments performed with our AFM set-up show that the proposed RC significantly outperforms a conventional PI controller that is typically used for the same task. The scan error and the average tapping forces are reduced by 66% and 58%, respectively when the scan speed is increased by 7-fold.