Automatic tuning of PI controller for atomic force microscope based on relay with hysteresis

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.