Design and implementation of an atomic force microscope with adaptive sliding mode controller for large image scanning

Atomic force microscopy (AFM) is an advanced technique which aims to scan a sample through the use of a probe or a tip; however, conventional atomic force microscope system suffers from the limitation of small scanning range, due to the short travelling range of piezoelectric actuation. In this paper, we propose a large measurement- range AFM scanning system which combines both fine positioners of piezoelectric and electromagnetic actuations. While the piezoelectric positioner provides high speed scanning with nanometer resolution, the precision electromagnetic positioner is capable of 1 mm² large field positioning with 30 nm rms error. The overall design of the stage consists of 4 pairs of electromagnetic actuator, monolithic serial flexure guidance with compression springs, an eddy current damper, and a commercial xyz piezoelectric positioner. Besides, a stationary compact disk/digital versatile disk pick-up-head (CD/DVD PUH) is used to measure the amplitude of samples. Moreover, an adaptive sliding mode controller based on the analytical modeling is used to overcome the unmodeled system uncertainties and external disturbances. Finally, preliminary experiments are presented, demonstrating feasibility of the proposed system.