AN AFM PROBE CONTROLLER DESIGN BASED ON μ-SYNTHESIS

摘要

The atomic force microscope (AFM) is one of the most important tools for measuring atomic resolution. The AFM system maintains constant force between a tip and the sample in order to track the sample topography. The controller that maintains the constant interaction force plays a significant role in measurement accuracy. This paper presents a μ-synthesis controller design to deal with model uncertainty and establish a measurement error bound. The system's nonlinearity and the set-point drift are lumped into a multiplicative uncertainty. The performance bound allows specification of the error magnitude over the frequency range. Simulation results show that the proposed control can tolerate uncertainties. The error spectrum from the experiments shows consistency with the design specifications. Images were taken to compare μ-synthesis control with a well-tuned PID control at a 480μm/s scan rate. The results verify the outstanding performance of the μ-controller.