1,721,214 research outputs found
Adaptive unit-vector control of an uncertain heat diffusion process
No full textThis paper deals with the distributed tracking control of a heat process having uncertain diffusivity and subject to a distributed disturbance whose L2 norm is bounded by a constant which is not known a priori. Under certain regularity assumptions on the disturbance and on the chosen reference profile, a distributed unit-vector control, with an adaptive magnitude, is designed which provides the asymptotic tracking of the reference. The logic governing the gain adaptation is gradient-based and monodirectional, i.e. the gain cannot decrease over time. Lyapunov arguments are invoked to support the convergence properties of the proposed scheme, whose performance are also investigated by means of computer simulation
On the multi-input second-order sliding mode control of nonlinear uncertain systems
No full textThis note addresses the multi-input second-order sliding mode control design for a class of nonlinear multivariable uncertain dynamics. Among the most important peculiarities of the considered control problem, the considered sliding vector variable has a uniform vector relative degree [2,2, â∥,2] with respect to the vector control variable, and only the sign of the sliding vector and of its derivative are available for feedback. Additionally, the symmetric part of the state-dependent control matrix is supposed to be positive definite. Under some further mild restrictions on the uncertain system's dynamics, a control algorithm that realizes a multi-input version of the 'twisting' second-order sliding mode control algorithm is suggested. Simple controller tuning conditions are derived by means of a constructive Lyapunov analysis, which demonstrates that the suggested control algorithm guarantees the semiglobal asymptotic convergence to the sliding manifold. Simulation results, which confirm the good performance of the proposed scheme and investigate the actual accuracy obtained under the discrete-time implementation effects, are given
BLACK-BOX POSITION AND ATTITUDE TRACKING FOR UNDERWATER VEHICLES BY SECOND-ORDER SLIDING-MODE TECHNIQUE
No full textOutput-Feedback Regulation of the Contact-Force in the High-Speed Train Pantographs
No full textOne of the main problems in high-speed train transportation systems is to counteract the fast variations of the contact force between the catenary and the pantograph collector end. The variation of the catenary equivalent stiffness, due to the suspending system, originates mechanical oscillations whose frequency and magnitude are larger and larger as the train speed increases. Such oscillations cause electric arcs that damage the mechanical structure and compromise the collection of the current from the supply wire, degradating the overall performance. Active pantographs offer the possibility of affecting the contact force evolution by suitably modifying the control torque applied to the lower arm of the pantograph. We consider the equivalent stiffness of the catenary as an uncertainty to compensate for by suitable robust control techniques, and , under the assumption that a noisy measurement of the contact force is available, we propose an output feedback control scheme based on higher-order sliding modes and high-gain observers. That combination allows for an almost complete rejection of the undesired oscillations of the contact force, as confirmed by simulations, and it is very attractive for real-time implementation purposes, due to its simplicity and robusteness
Globally convergent real-time differentiation via second order sliding modes
No full textIn this article the design of a new real-time differentiator featuring global convergence properties is considered. Such a problem is tackled by means of a second-order sliding mode differentiator (2-SMD) with adjustable gain and switching logic. Due to its finite time convergence and relaxed information demand regarding the signal to differentiate, the proposed differentiator appears well suited to be combined with output-feedback controllers. In order to point out the effectiveness and the convergence features of the proposed 2-SMD, some simulations related to a global output feedback stabilisation problem are presented
Robust control of container cranes: theory and experimental validation
No full textFast and swing-free transfer of a suspended load is not easy to obtain in the presence of model uncertainties (e.g. unknown load mass) and disturbances. In this paper, we exploit the positive features that characterize the second-order sliding-mode approach to design a simple control system which, unlike other approaches, guarantees the suppression of the load swing during transport and precise final positioning by relying on a weak amount of information about the crane and load parameters. The trolley position, the rope length and the swing angle are the only measured quantities and, for feedback, the controller also uses estimates of the trolley and rope velocities provided by real-time sliding-mode differentiators. The features of the observer-controller scheme and the relevant implementation issues are discussed, and some results from experiments carried out on a laboratory-sized overhead crane model are provided
GLOBAL OUTPUT-FEEDBACK TRACKING AND LOAD DISTURBANCE REJECTION FOR ELECTRICALLY-DRIVEN ROBOTIC MANIPULATORS WITH UNCERTAIN DYNAMICS
No full text
Contact force regulation in wire-actuated pantographs via variable structure control and frequency-domain techniques
No full textOne of the main problems in high-speed-train transportation systems is related to the current collection quality, that can dramatically decrease because of oscillations of the pantograph-catenary system. This problem has been addressed by means of active pantographs. In this paper we present some results about the possible implementation of variable structure control (VSC) techniques on a wire actuated symmetric pantograph. Such an actuator was suggested in the literature as a viable solution to building an active pantograph by modifying a passive pantograph currently used by Italian Railways. The use of VSC with sliding modes was considered in order to cope with the system uncertainties due to the overhead suspended catenary. Recent results about the frequency-based analysis of VSC systems featuring second-order sliding modes are exploited to avoid the performance-destroying effect of the resonant wire actuator and to get a continuous control force without using observers. We show by simulations that the contact force results are very close to the desired set-point also in the presence of measurement noise
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