Creep, hysteresis, and vibration effects attenuation in an AFM PTS

There is a need, in the wide ranging scientific community, to perform fast scans using atomic force microscope (AFM) with nanoscale accuracy. The performance of AFM at high scanning speeds is limited due to some serious limitations of its scanning unit; i.e., the piezoelectric tube scanner (PTS). In order to increase the imaging speed of an AFM, a multi-input multi-output (MIMO) model predictive control (MPC) scheme is applied to the axes of the PTS to reduce its creep, hysteresis, and vibration effects. The design of this controller is based on an identified MIMO model of the AFM PTS. Also, a vibration compensator is designed and included in the feedback loop with the plant to suppress the vibration of the PTS at the resonant frequency. To evaluate the performance improvement achieved using the proposed control scheme, experimental comparisons of the scanned images obtained using open-loop and the in-built proportional-integral (PI) controller is made. The comparison demonstrates the usefulness of the proposed controller.