Marialena Vagia

Damping and Tracking Control Schemes for Nanopositioning

Fast and accurate tracking of reference trajectories is highly desirable in many nanopositioning applications, including scanning probe microscopy. Performance in common positioning stage designs is limited by the presence of lightly damped resonances and actuator nonlinearities such as hysteresis and creep. To improve the tracking performance in such systems, several damping and tracking control schemes have been presented in the literature. In this paper, six different control schemes are presented and applied to a nanopositioning system for experimental comparison. They include schemes applying damping control in the form of positive position feedback, integral resonant control, integral force feedback, and passive shunt-damping. Also, general pole placement in the form of model reference control, as well as a control scheme requiring only a combination of a low-pass filter and an integrator, is presented. The control schemes are fixed-structure, low-order control laws, for which few results exist in the literature with regard to optimal tuning. A practical tuning procedure for obtaining good tracking performance for five of the control schemes is, therefore, presented. Experimental results show that the schemes provide similar performance, and the main differences are due to the specific implementation of each scheme.

A literature review on the levels of automation during the years. What are the different taxonomies that have been proposed

In this paper we present a literature review of the evolution of the levels of autonomy from the end of the 1950s up until now. The motivation of this study was primarily to gather and to compare the literature that exists, on taxonomies on levels of automation. Technical developments within both computer hardware and software have made it possible to introduce autonomy into virtually all aspects of human-machine systems. The current study, is focusing on how different authors treat the problem of different levels of automation. The outcome of this study is to present the differences between the proposed levels of automation and the various taxonomies, giving the potential users a number of choices in order to decide which taxonomy satisfies their needs better. In addition, this paper surveys deals with the term adaptive automation, which seems to be a new trend in the literature on autonomy.

Intelligent Robust Controller Design for a Micro-Actuator

In this article the design of an intelligent robust controller for a micro-actuator is presented. The μ-actuator is composed of a micro-capacitor, whose one plate is clamped while its other flexible plate’s motion is constrained by hinges acting as a combination of springs and dashpots. The distance of the plates is varied by the applied voltage between them. The dynamics of the plate’s rigid-body motion results in an unstable, nonlinear system. The control structure is constructed from: (a) a feedforward controller which stabilizes the micro-actuator around its nominal operating point, (b) a robust PID controller with its gains tuned via the utilization of Linear Matrix Inequalities (LMIs), and (c) an intelligent prefilter which shapes appropriately the reference signal. The resulting overall control scheme is applied to the non-linear model of the μ-actuator where simulation results are presented to prove the efficacy of the suggested scheme.

A literature review on modeling and control design for electrostatic microactuators with fringing and squeezed film damping effects

A literature review concerning the modeling and control design aspects of electrostatic micro-actuators is presented in this article. The modeling issues of electrostatic micro actuators with fringing and squeezed film damping effects are presented followed by control strategies that have already been applied in such systems. As a special use, the analytic model and suboptimal robust control of a micro Cantilever Beam (μCB) with fringing and squeezed thin film damping effects is presented. The suspended clamped-free μCB can move via the application of an external electrically induced force. The nonlinear model of the μCB is linearized in multiple operating points with respect to the beams tip-end displacement. A robust H∞-controller relying on the LMI-theory is designed for the set of the resulting multiple operating models. Particular attention is paid in order to examine the stability issue within the intervals of the operating points. Simulation results investigate the efficacy of the suggested modeling and control techniques.

LMI-region pole placement control scheme for an electrostatically actuated micro Cantilever Beam

In the present article the modeling and control design aspects of a narrow micro Cantilever Beam (μCB) with fringing and squeezed thin film damping effects are presented. The suspended clamped-free μCB can move via the application of an external electrically induced force. The nonlinear model of the μCB is linearized at multiple operating points with respect to the beams displacement. An LMI-region based pole placement controller is designed for the set of the resulting multiple operating models. Particular attention has been paid in order to examine the effects of the systems pressure variations. In addition, variations of the LMI-region where the closed loop poles lie, are investigated in order to check changes in critical characteristics of the closed loop system such like velocity, transient effects etc. Numerous test cases have been applied on the μCBs model and simulation results prove the efficacy of the suggested modeling and control techniques.

Fault Detection using Set Membership Identification for Micro-Electrostatic Actuators

Fault detection in micro-electrostatic actuators caused primarily by their mechanical components (combs, thin air-damping) is investigated in this article. The system is assumed to be linearly parameterizable and the parameter vector contains the quantities that are susceptible to faults. While the system is operating in a closed-loop configuration, a set-membership identifier monitors the feasible region within which the nominal parameters should reside. The hyper-volume of this region is a measure of the uncertainty of the system parameters and decreases in a monotonic manner with time. A fault is detected when: a) there is a sudden increase in this volume, or b) when the identified centroid of the parameter vector resides out of the feasible region, or c) when the systems output is out of its allowable predicted bounds. Simulation studies are offered to test the efficiency of the suggested fault-detection method.

How to extend the travel range of a nanobeam with a robust adaptive control scheme: A dynamic surface design approach

In this study, an adaptive robust tracking control scheme for a nanomechanical beam is proposed. The mathematical nanobeam model takes into consideration the presence of parametric uncertainties, and external disturbances, and fringing field effects and intermolecular forces, are also incorporated. The proposed backstepping controller is enhanced with an adaptive dynamic surface technique and an H(∞) control scheme. The overall effectiveness of the designed controller is checked and illustrated with the presented results. These results show that the desired transient output tracking performance is achieved, and that the closed loop system exhibits good robustness to system uncertainties. Particular attention has been paid, so as to identify any relevance between the variations in the controllers design parameter and the systems output response and performance.

Modeling aspects and gain scheduled H ∞ controller design for an electrostatic micro-actuator with squeezed gas film damping effects

In this article the modeling and control design aspects of an electrostatic microactuator (EmA) with squeezed thin film damping effects are presented. The modeling analysis of the squeezed film damping effect is investigated in the case of an EmA composed by a set of two plates. The bottom plate is clamped to the ground, while the moving plate is driven by an electrically induced force which is opposed by the force exerted by a spring element. The nonlinear model of the EmA is linearized at various operating points, and the feedforward compensator provides the nominal voltage. Subsequently a gain scheduled H∞ controller is used to tune the controller-parameters depending on the EmAs operating conditions. The controller is designed at various operating points based on the distance between its plates. The parameters of the controller are tuned in an optimal manner and computed via the use of the Linear Matrix Inequalities. Special attention is paid in order to examine the stability issue in the intervals between the operating points. Simulation results investigate the efficacy of the suggested modeling and control techniques.

Robust PID-control design for an electrostatic micromechanical? actuator with structured uncertainty

In this article, a robust PID controller coupled to a feedforward compensator is designed for set-point regulation maneuvers of an electrostatic micromechanical system. The system is linearized at multiple operating points, and the feedforward compensator provides the nominal voltage. Perturbations around these points, are handled from the PID-controller, whose gains are tuned via the utilization of an LMI-approach which guarantees robustness against the switching nature of the linearized system dynamics. The maximum microspring-stiffness parametric uncertainty that can be tolerated within this scheme, is computed through the use of the small-gain theorem. Simulation studies are presented that proves the efficacy of the suggested scheme.

Autonomous Job Analysis a method for design of autonomous marine operations

Increased use of autonomy is considered crucial for continued growth in maritime industries like oil- and gas, waterborne transport, and fisheries- and aquaculture. This article presents a method called Autonomous Job Analysis (AJA), which purpose is to guide the design of autonomous marine operations. AJA breaks down the operation, and focuses on autonomy early in the design phase. The method uses elements from Hierarchical Task Analysis (HTA), and the execution of the analysis is influenced by HAZard and OPerability (HAZOP) studies. The proposed method is illustrated through application on two different case studies: Inspection of mooring lines in a sea-based fish-farm, and imaging of plume extension caused by discharge from a waste water plant.