Feedforward control of piezoactuators in atomic force microscope systems

This article describes an inversion-based feedforward approach to compensate for dynamic and hysteresis effects in piezoactuators with application to AFM technology. To handle the coupled behavior of dynamics and hysteresis, a cascade model is presented to enable the application of inversion-based feedforward control. The dynamics, which include vibration and creep, are modeled using linear transfer functions. A frequency-based method is used to invert the linear model to find an input that compensates for vibration and creep. The inverse is noncausal for nonminimum-phase systems. Similarly, the hysteresis is handled by an inverse-Preisach model. To avoid the complexity of finding the inverse-Preisach model, high- gain feedback control can be used to linearize the system's behavior. A feedforward input is then combined with the feedback system to compensate for the linear dynamics to achieve high-speed AFM imaging. Finally, recent efforts in feedforward control for an SPM application including the use of iteration to handle hysteresis as well as uncertainties and variations in the system model is discussed.