Dual actuation for high speed atomic force microscopy

In atomic force microscopy (AFM) the imaging speed is strongly limited by the bandwidth of the feedback loop that controls the interaction between the measurement tip and the sample. A significant increase in closed-loop bandwidth can be achieved by combining a long-range, low-bandwidth actuator with a short-range, high-bandwidth actuator, forming a dual actuated system. This contribution discusses the design of a model-based feedback controller that controls the tip-sample interaction in dual actuated AFM. In order to guarantee closed-loop stability, the dynamic uncertainties of the system are identified and taken into account in the controller design. Two different design cases are discussed, showing the trade-off between the positioning range at lower frequencies and the positioning range at higher frequencies. The designed feedback controller is implemented on the prototype AFM system and demonstrates a disturbance rejection bandwidth of 20 kHz.