Inversion-based control tools for high-speed precision  tracking/transition in emerging applications
Creators: name: Wang, Haiming
Publisher: name: No Publisher Supplied
Year: 2013

description: This dissertation work is motivated by the challenges in high-speed precision output tracking  and transition in emerging applications, particularly for nonminimum-phase systems. Although  fundamental performance limits to achieving precision output tracking with feedback  control alone have been studied and quantified, for nonminimum-phase systems, exact output  tracking cannot be achieved by using feedback control alone, due to the limits imposed  by the nonminimum-phase zeros of the system. On the feedforward control side, the stable  inversion theory solved the challenging output tracking problem and achieved exact tracking  of a given desired output trajectory for nonminimum-phase systems (linear and nonlinear).  The obtained solution, however, is noncausal and requires the entire desired trajectory to be  known a priori. This noncausality constraint has been alleviated through the development of  the preview-based inversion approach. Therefore, the stable-inversion framework provides an  effective approach to output tracking of nonminimum-phase systems. Challenges, however,  still exist in the existing stable-inversion theory for continuously more stringent control requirements.  For example, the control problem of nonperiodic tracking-transition switching  with preview for nonminimum-phase systems cannot be satisfactorily addressed by using the  existing techniques. Another challenge in the existing stable-inversion approach is that as a  feedforward control technique, it can be sensitive to the system dynamics uncertainties. Finally,  the demanding online computation involved in the preview-based stable-inversion technique  hinders the application of this approach in the presence of limited computation power.  Therefore, these challenges, as magnified in applications of high-speed nano-manipulation and  nano-fabrication, motivate the research work of this dissertation. First, the problem of nonperiodic  tracking-transition switching with preview is considered. In the proposed preview-based  optimal output tracking and transition (POOTT) approach, the optimal desired output trajectory  for the transition sections is designed through direct minimization of the output energy,  and the needed control input is obtained to maintain the smoothness of system state across all tracking-transition switching instants by using a preview-based stable-inversion approach.  The needed preview time is quantified, and the recently-developed optimal preview-based inversion  approach is also incorporated to minimize the amount of preview time. Secondly, a  B-spline-decomposition (BSD)-based approach to output tracking with preview is developed  for nonminimum-phase systems, that not only substantially reduces the dynamics uncertainty  effect on tracking performance, but also minimizes the online demanding computation. The  BSD approach is illustrated through simulation study of a nanomanipulation application using  a nonminimum-phase piezo actuator model, and then further demonstrated by a 2D nanomanipulation  in experiments using AFM. Finally, a multi-axis inversion-based iterative control  (MAIIC) approach is developed to compensate for the dynamics coupling in multi-axis motion  during high-speed nanofabrication. By using this advanced control technique, precision  position control of the probe with respect to the sample substrate can be achieved during highspeed,  large-range multi-axis nanofabrication. Particularly, the cross-axis dynamics coupling  effect on the output tracking can be compensated for during the iterative learning process with  no additional steps to learn the cross-coupling effect separately. The MAIIC approach is illustrated  through experiments by implementing it to fabricate two Chinese characters pattern  via mechanical scratching on a gold-coated silicon sample surface at high speed. The research  work of this dissertation addresses the limits and further extends the inversion-based control  techniques for high-speed precision tracking/transition in emerging applications, particularly,  the challenges involved in output tracking with non-periodic tracking-transition switching, accounting  for dynamics uncertainty and demanding computation requirements for nonminimum-phase  systems, and cross-axis coupling in high-speed multi-axis motion. The experimental part  of the work demonstrates and illustrates the efficacy of the proposed control techniques.