Robust Control of Atomic Force Microscopy, Mechatronics by Paulo Davim

B. Aksun Guvenc, S. Necipoglu, B. Demirel and L. Guvenc

Abstract

The Atomic Force Microscope (AFM) is an instrument used for acquiring images at nanometer scale. Obtaining better image quality at higher scan speed is a research area of great interest in the control of an AFM. Improving the dynamic response of the scanning probe in the vertical direction and the dynamic response of the scanning motion in the lateral plane are the two major areas of application of advanced control methods to an AFM. The uncertainties inherent in the models of AFM vertical and lateral direction motion stages dictates the application of robust control methods. This chapter applies robust control methods to atomic force microscopy, treating first the vertical direction and then the lateral plane. Improving the AFM stage dynamics is achieved either by designing stages with higher bandwidth or designing more sophisticated controllers rather than the PI, PID or PIID types of controllers that are most commonly used in practice. A robust repetitive controller is used for the vertical direction as it can reject higher frequency disturbances due to the periodic part of the surface topography in AFM much better than a conventional controller can. Besides increasing the scan speed, it is also important that the phase lag can be compensated perfectly using repetitive control, with the knowledge of the surface topography from the previous period by introducing appropriate phase advance into the controller. Next, a multi-input-multi-output (MIMO) extension of the disturbance observer control method is applied to the lateral plane of scanning motion in a piezoelectric tube based atomic force microscope. Calibration free and decoupled operation of the AFM is achieved with this technique. The technique is also robust to creep and hysteresis effects that are common in piezoelectric actuators. Both the repetitive and MIMO disturbance observer controllers are designed using the COMES - Control of Mechatronic Systems Toolbox.

@article{GND++:11,
  Author = {B. Aksun Guvenc and S. Necipoglu and B. Demirel and L. Guvenc},
  Title = {Robust Control of Atomic Force Microscopy},
  Journal = { },
  Volume = { }
  Number{ }
  Pages = { }
  Year = {2011}
}