We study the dynamics of a ring of unidirectionally coupled autonomous Duffing oscillators. Starting from a situation where the individual oscillator without coupling has only trivial equilibrium dynamics, the coupling induces complicated transitions to periodic, quasiperiodic, chaotic, and hyperchaotic behavior. We study these transitions in detail for small and large numbers of oscillators. Particular attention is paid to the role of unstable periodic solutions for the appearance of chaotic rotating waves, spatiotemporal structures, and the Eckhaus effect for a large number of oscillators. Our analytical and numerical results are confirmed by a simple experiment based on the electronic implementation of coupled Duffing oscillators.

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In numerous electric drive applications, the mechanical phenomena in the velocity or position control loop determine real difficulties and challenges for the control system. So-called two-mass drive systems with a flexible shaft are the most important example of this situation. The problem becomes even more difficult if the characteristics of torque transmission along the shaft are nonlinear, nonlinear friction is present, and the plant parameters are unknown, as it happens in numerous robotic systems. A novel adaptive controller is derived for such a system. The recurrent design procedure is based on proper modifications of the adaptive backstepping scheme, including non-strict-feedback plant application, tuning functions to exclude controller overparameterization, robust adaptive laws, proper means to avoid controller complexity explosion, and a nonlinear PI controller in the initial loop to minimize quasi-steady-state tracking error. The closed-loop system uniform ultimate boundedness is proven using Lyapunov techniques and the design and tuning procedures are described. The attractive features of the obtained drive, including the robustness against the violation of assumptions, are presented using several examples.

The paper describes a nonlinear controller design technique for a servo drive in the presence of nonlinear friction together with a flexible shaft connecting the motor and the load. The shaft is characterized by the nonlinear stiffness curve. Two different type of the nonlinear stiffness curve are considered. The proposed controller is based on adaptive backstepping, modified by the use of command filtering. The proposed approach allows to accomplish the rigorous proof of the closed-loop system stability. Several experiments prove the control effectiveness. Sterszczenie. Opisano problem sterowania prędkością układu napędowego z nieliniowym tarciem, połączeniem sprężystym i nieznanymi parametrami. Elastyczne połączenie jest opisane przy pomocy nieliniowej funkcji sztywności. Rozważane są dwa typy nieliniowej funkcji sztywności: wypukła i wklęsła. Układy regulacji są projektowane przy pomocy metod "adaptive backstepping" z filtracją wartości zadanych. Opisano szereg eksperymentów, które ilustrują charakterystyczne właściwości układu regulacji. (Adaptacyjne sterowanie dwu-masowego układu napędowego z nieliniową charakterystyką sztywności)

In this study, the problem of master–slave synchronization of two different chaotic systems is considered and solved under a novel set of assumptions. The mathematical model of each of them contains unknown, constant parameters. Only a single output of the master system is available, and only a single input of the slave system is a control input. The proposed, novel approach is based on the active cooperation of the adaptive observer of the master system and adaptive controller of the slave. The tuning function technique is included in the observer–controller design to avoid overparameterization. Complexity explosion and unacceptable increases in adaptive parameters are prevented by proper adaptive techniques application. Due to the selected observer type, the derivation is restricted to the defined class of master systems—output-nonlinear parametric (ONP) systems. Linear transformation of several popular chaotic systems (e.g., Arneodo, Arneodo–Coullet, Genesio–Tesi, Lur’e) into the ONP form is discussed. The stability of the whole, closed-loop system is derived using Lyapunov techniques and examples of implementation (synchronization of Arneodo and 3D jerk systems) are provided.