A. Doris

Observer Designs for Experimental Non-Smooth and Discontinuous Systems

This brief presents the design and implementation of observer design strategies for experimental non-smooth continuous and discontinuous systems. First, a piece-wise linear observer is implemented for an experimental setup consisting of a harmonically excited flexible steel beam with a one-sided support which can be considered as a benchmark for a class of flexible mechanical systems with one-sided restoring characteristics. Second, an observer is developed for an experimental setup that describes a dynamic rotor system which is a benchmark for motion systems with friction and flexibility. In both cases, the implemented observers guarantee global asymptotic stability of the estimation error dynamic in theory. Simulation and experimental results are presented to demonstrate the performance of the observers in practice. These results support the use of (switched) observers to achieve state reconstruction for such non-smooth and discontinuous mechanical systems.

Switching observer design for an experimental piece-wise linear beam system

This paper presents an implementation of a switching observer design strategy to a piece-wise linear beam system comprising a flexible steel beam with a one-sided support. The switching observer design strategy guarantees asymptotic stability of the estimation error. Experimental and simulation results are presented to demonstrate the observer error stability and performance.

A disturbance attenuation approach for a class of continuous piecewise affine systems : control design and experiments

We consider the disturbance attenuation problem for a class of continuous piecewise affine systems. Hereto, observer-based output-feedback controllers are proposed that render the closed-loop system uniformly convergent. The convergence property ensures, first, stability and, second, the existence of a unique, bounded, globally asymptotically stable steady-state solution for each bounded disturbance. The latter property is key in uniquely specifying closed-loop performance in terms of disturbance attenuation. Because of its importance in engineering practice, the class of harmonic disturbances is studied in particular and performance measures for this class of disturbances are proposed based on so-called generalized frequency response functions for convergent systems. Additionally, the derived control strategy is extended by including conditions that guarantee the satisfaction of a bound on the control input. The effectiveness of the proposed control design strategy is illustrated by the application of the results to an experimental benchmark system being a piecewise affine beam system.

Active disturbance attenuation for an experimental piecewise linear beam system

Abstract This paper presents an experimental implementation of an observer-based controller design strategy on a piecewise linear beam system comprising a flexible steel beam with a one-sided support. The observer-based controller design strategy guarantees a unique globally asymptotically stable steady-state solution of the closed-loop system, which allows for unique performance evaluation in terms of disturbance attenuation. Experimental and simulation results are presented to demonstrate the effectiveness of the strategy.

Experimental Validation of Torsional Controllers for Drilling Systems

Torsional stick-slip vibrations decrease the performance, reliability and fail-safety of drilling systems used for the exploration and harvesting of oil, gas, minerals and geo-thermal energy. Current industrial controllers regularly fail to eliminate stick-slip vibrations, especially when multiple torsional flexibility modes in the drill-string dynamics play a role in the onset of stick-slip vibrations. This chapter presents the experimental validation of novel robust output-feedback controllers designed to eliminate stick-slip vibrations in the presence of multiple dominant torsional flexibility modes. For this purpose, a representative experimental test setup is designed, using a model of a real-life drilling rig as a basis. The model of the dynamics of the experimental setup can be cast in Lur’e-type form with set-valued nonlinearities representing an (uncertain) model for the complex bit-rock interaction and the interaction between the drill-string and the borehole. The proposed controller design strategy is based on skewed-\(\mu \)-DK-iteration and aims at optimizing the robustness with respect to uncertainty in the non-smooth bit-rock interaction. Moreover, a closed-loop stability analysis for the non-smooth drill-string model is provided. Experimental results confirm that stick-slip vibrations are indeed eliminated using the designed controller in realistic drilling scenarios in which state-of-practice controllers have failed to achieve the same.

Mitigation of Torsional Vibrations in Drilling Systems: A Robust Control Approach

Stick-slip vibrations decrease the performance, reliability, and fail safety of drilling systems. The aim of this paper is to design a robust output-feedback control approach to eliminate torsional stick-slip vibrations in drilling systems. Current industrial controllers regularly fail to eliminate stick-slip vibrations, especially when multiple torsional flexibility modes play a role in the onset of stick-slip vibrations. As a basis for controller synthesis, a multimodal model of the torsional dynamics for a real drill-string system is employed. The proposed controller design strategy is based on skewed-

Experimental results on output-feedback control of a nonsmooth rotor dynamic system

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Control of mechanical motion systems with non-collocation of actuation and friction: A Popov criterion approach for input-to-state stability and set-valued nonlinearities

DK iteration and aims at optimizing the robustness with respect to uncertainty in the nonlinear bit–rock interaction. Moreover, a closed-loop stability analysis for the nonlinear drill-string model is provided. This controller design strategy offers several benefits compared with existing controllers. First, only surface measurements are employed, therewith avoiding the need for down-hole measurements. Second, multimodal drill-string dynamics are effectively dealt with in ways inaccessible to state-of-practice controllers. Third, robustness with respect to uncertainties in the bit–rock interaction is explicitly provided and closed-loop performance specifications are included in the controller design. Case study results confirm that stick-slip vibrations are indeed eliminated in realistic drilling scenarios using the designed controller in which state-of-practice controllers fail to achieve this.

Output-feedback design for non-smooth mechanical systems : control synthesis and experiments

There is disclosed a polyurethane/unsaturated polyester hybrid foam of the rigid type prepared from novel components including not only polyol and polyisocyanate but also a unique hydroxy-containing vinyl ester and vinyl monomer, optionally together with an additional polar vinyl monomer, all together providing the necessary components for a hybrid polyurethane-polyvinyl ester matrix, which mixture of components before foaming is capable of having suspended therein fillers and reinforcing fibers to produce a foam or reinforced foam composite having a density between about 20 and 100 pounds per cubic foot. The reinforced foam can be made into baords and the like and advantageously has continuous fiberglass strands or yarn disposed longitudinally in or adjacent the surface skin of the foam. The strands or yarn are preferably parallel and close together and are preferably flattened out in the foam-forming process so that the surfaces have a continuous fiberglass implant longitudinally and substantially so transversely. One preferred structural composite is illustrated in the drawings.