A robust loop-shaping approach to fast and accurate nanopositioning

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Butterworth Pattern-based Simultaneous Damping and Tracking Controller Designs for Nanopositioning Systems

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Fuzzy-enhanced Dual-loop Control Strategy for Precise Nanopositioning

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Global fast non-singular terminal sliding-mode control for high-speed nanopositioning

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Evaluating the performance of robust controllers for a nanopositioning platform under loading

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Modeling and Control of Piezoactive Micro and Nano Systems

Piezoelectrically-driven (piezoactive) systems such as nanopositioning platforms, scanning probe microscopes, and nanomechanical cantilever probes are advantageous devices enabling molecular-level imaging, manipulation, and characterization in disciplines ranging from materials science to physics and biology. Such emerging applications require precise modeling, control and manipulation of objects, components and subsystems ranging in sizes from few nanometers to micrometers. This dissertation presents a comprehensive modeling and control framework for piezoactive micro and nano systems utilized in various applications. The development of a precise memory-based hysteresis model for feedforward tracking as well as a Lyapunov-based robust-adaptive controller for feedback tracking control of nanopositioning stages are presented first. Although hysteresis is the most degrading factor in feedforward control, it can be effectively compensated through a robust feedback control design. Moreover, an adaptive controller can enhance the performance of closed-loop system that suffers from parametric uncertainties at high-frequency operations. Comparisons with the widely-used PID controller demonstrate the effectiveness of the proposed controller in tracking of high-frequency trajectories. The proposed controller is then implemented in a laser-free Atomic Force Microscopy (AFM) setup for high-speed and low-cost imaging of surfaces with micrometer and nanometer scale variations. It is demonstrated that the developed AFM is able to produce high-quality images at scanning frequencies up to 30 Hz, where a PID controller is unable to present acceptable results. To improve the control performance of piezoactive nanopositioning stages in tracking of time-varying trajectories with frequent stepped discontinuities, which is a common problem in SPM systems, a supervisory switching controller is designed and integrated with the proposed robust adaptive controller. The controller switches between two control modes, one mode tuned for stepped trajectory tracking and the other one tuned for continuous trajectory tracking. Switching conditions and compatibility conditions of the control inputs in switching instances are derived and analyzed. Experimental implementation of the proposed switching controller indicates significant improvements of control performance in tracking of time-varying discontinuous trajectories for which single-mode controllers yield undesirable results. Distributed-parameters modeling and control of rod-type solid-state actuators are then studied to enable accurate tracking control of piezoactive positioning systems in a wide frequency range including several resonant frequencies of system. Using the extended Hamilton\u27s principle, system partial differential equation of motion and its boundary conditions are derived. Standard vibration analysis techniques are utilized to formulate the truncated finite-mode state-space representation of the system. A new state-space controller is then proposed for asymptotic output tracking control of system. Integration of an optimal state-observer and a Lyapunov-based robust controller are presented and discussed to improve the practicability of the proposed framework. Simulation results demonstrate that distributed-parameters modeling and control is inevitable if ultra-high bandwidth tracking is desired. The last part of the dissertation, discusses new developments in modeling and system identification of piezoelectrically-driven Active Probes as advantageous nanomechanical cantilevers in various applications including tapping mode AFM and biomass sensors. Due to the discontinuous cross-section of Active Probes, a general framework is developed and presented for multiple-mode vibration analysis of system. Application in the precise pico-gram scale mass detection is then presented using frequency-shift method. This approach can benefit the characterization of DNA solutions or other biological species for medical applications

High-precision Control of a Piezo-driven Nanopositioner Using Fuzzy Logic Controllers

Acknowledgments: The authors would like to thank Douglas Russell for the technical help and Andres San-Millan for data measurements. Financial support via the Elphinstone Research Scholarship, provided by the School of Engineering, University of Aberdeen, to fund Mohammed Altaher’s Ph.D. work is highly appreciated.Peer reviewedPublisher PD

Two-degrees-of-freedom PI2D controller for precise nanopositioning in the presence of hardware-induced constant time delay

This work was supported in part by the Spanish Agencia Estatal de Investigacion (AEI) under Project DPI2016-80547-R (Ministerio de Economia y Competitividad) and in part by the European Social Fund (FEDER, EU), and in part by the Spanish FPU12/00984 Program (Ministerio de Educacion, Cultura y Deporte).Peer reviewedPostprin

Enhanced Positioning Bandwidth in Nanopositioners via Strategic Pole Placement of the Tracking Controller

Funding: This research received no external funding.Peer reviewedPublisher PD

High-bandwidth nanopositioning via active control of system resonance

Acknowledgements This work was supported in part by the National Natural Science Foundation of China (Grant Nos. U2013211 and 51975375), the Open Foundation of the State Key Laboratory of Fluid Power and Mechatronic Systems, China (Grant No. GZKF-202003), and the Binks Trust Visiting Research Fellowship (2018), University of Aberdeen, UK, awarded to Dr. Sumeet S. Aphale.Peer reviewedPublisher PD