  A major challenge in Atomic Force Microscopy (AFM) is to reduce the scan
duration while retaining the image quality. Conventionally, the scan rate is
restricted to a sufficiently small value in order to ensure a desirable image
quality as well as a safe tip-sample contact force. This usually results in a
conservative scan rate for samples that have a large variation in aspect ratio
and/or for scan patterns that have a varying linear velocity. In this paper, an
adaptive scan scheme is proposed to alleviate this problem. A scan line-based
performance metric balancing both imaging speed and accuracy is proposed, and
the scan rate is adapted such that the metric is optimised online in the
presence of aspect ratio and/or linear velocity variations. The online
optimisation is achieved using an extremum-seeking (ES) approach, and a
semi-global practical asymptotic stability (SGPAS) result is shown for the
overall system. Finally, the proposed scheme is demonstrated via both
simulation and experiment.

Signal Processing