Paul Ager

PhD Student
School of Computing, Engineering & Built Environment
Nanopositioning is the science of understanding and manipulation of matter at nanoscale level (100 micrometre or less). Nanopositioning devices and schemes have produced notable interest in the past decades, enabling research in nanotechnology with scanning probe microscopy as a major tool. This group of microscopes allows researchers to learn and manipulate matter at the molecular and atomic levels. Piezoelectric stack-actuated nanopositioners are appropriate for this application due to their simple construction, large motion range, cross-coupling and ease of control. Today, diverse designs of piezoelectric stack-actuated nanopositioning applications are handy commercially. The dominant resonant mode of these nanopositioners which exists at relatively low frequency is the major issue with their usage.
Undesired excitation of resonant frequencies can generate vibrations that can degrade the performance of the system substantially. Passive damping techniques do not require supervisory control or sensing but can be sensitive to system resonance frequencies that can limit their performance. Thus, active damping techniques seem more complicated but have the potential to overcome passive system performance limitation.
Various feedback controllers that impact substantial damping to the resonant system have been reported. Positive Position Feedback control (PPF), Resonant control, Shunt Damping (SD), Positive Velocity and Position Feedback (PVPF). Lack of robustness under changes in resonant frequencies, accurate system model design and high order control designs for multi-modes resonant system are some drawbacks associated with these techniques. They are fitting only for damping systems where the first mode is dominant over the subsequent modes. Integral Resonant control was proposed as a low-order simple scheme capable of damping multiple modes and keeping high-stability margins to overcome the problem associated with the other techniques.

Aim of the research:
• To Identify and implement methods of designing IRC, PPF and PVPF control schemes for SISO and extend such approach to multivariable process where applicable.
• To enhance the tracking performance of the piezo-driven nanopositioner through the implementation of control methods focussing on the area of interest in the desired trajectory. Also, utilizing Fuzzy logic or H-infinity or combining both as tracking controllers with IRC, PPF and PVPF. Such control structure has not been previously reported in the literature on controlling piezo-driven stages. It would be shown that fuzzy logic or H-infinity simplicity and accuracy in the study achieves the desired control purpose by providing smooth control action.
• To develop predictive and state-space methods of designing second order systems in nanotechnology.