Approach for improved positioning of an atomic force microscope piezoelectric tube scanner

There is a need, in the wide ranging scientific community, to perform fast scans using an atomic force microscope (AFM) with nanoscale accuracy. The performance of an AFM at high scanning speeds is limited because of some serious limitations of its scanning unit; that is, the piezoelectric tube scanner (PTS). To increase the imaging speed of an AFM, a multi-input-multi-output (MIMO) model predictive control scheme is applied in the axes of the PTS to reduce its vibration and cross-coupling effect. The design of this controller is based on an identified MIMO model of the AFM PTS. Moreover, a damping compensator is designed and included in the feedback loop with the plant to suppress the vibration of the PTS at the resonant frequency. Consequently, the proposed controller achieves a higher closed-loop bandwidth, significant damping of the resonant mode of the AFM PTS and results in compensation of the above effects. To evaluate the performance improvement using the proposed control scheme, an experimental comparison of its results with those of the AFM in-built proportional-integral controller is performed. This comparison shows the effectiveness of the proposed controller.