An atomic force microscope (AFM) usually employs proportional-integral (PI) control strategy to sustain a
constant cantilever deflection. However, it is well known that the tuning of PI parameters is a tedious and complicated
procedure, especially for those unfamiliar with control theory. In this paper, we employ and implement relay controller to
automate the tuning procedure for contact-mode AFM PI controller during different scanning speed operations based on
relay with hysteresis. Experimental results show that this approach offers system with satisfactory step response with
typical settling time of about 2 ms. Moreover, better sample topography image can be obtained after auto-tuning the control
gains during different scanning speed.