Hybrid Zero Dynamics of Planar Biped Walkers

Planar, underactuated, biped walkers form an important domain of applications for hybrid dynamical systems. This paper presents the design of exponentially stable walking controllers for general planar bipedal systems that have one degree-of-freedom greater than the number of available actuators. The within-step control action creates an attracting invariant set—a two-dimensional zero dynamics submanifold of the full hybrid model—whose restriction dynamics admits a scalar linear time-invariant return map. Exponentially stable periodic orbits of the zero dynamics correspond to exponentially stabilizable orbits of the full model. A convenient parameterization of the hybrid zero dynamics is imposed through the choice of a class of output functions. Parameter optimization is used to tune the hybrid zero dynamics in order to achieve closed-loop, exponentially stable walking with low energy consumption, while meeting natural kinematic and dynamic constraints. The general theory developed in the paper is illustrated on a five link walker, consisting of a torso and two legs with knees

Swarming behavior as Nash equilibrium

The question of whether swarms can form as a result of a non-cooperative game played by individuals is shown here to have an affirmative answer. A dynamic game played by N agents in one-dimensional motion is introduced and models, for instance, a foraging ant colony. Each agent controls its velocity to minimize its total work done in a finite time interval. The game is shown to have a Nash equilibrium that has all the features of a swarm behavior. © 2012 IFAC

Estudi comparatiu de la publicació científica de la UPC i l’ETSETB vs. altres universitats d’àmbit europeu (2002-2012)

L'informe es centra en la publicació científica especialitzada en l'àmbit temàtic propi de l'ETSETB: l'enginyeria de telecomunicacions i l'electrònica. Es comparen indicadors bibliomètrics de la UPC i l'ETSETB amb els d'altres universitats europees amb activitat de recerca notable en l'àrea de les telecomunicacions i l'electrònica.Postprint (author’s final draft

Estudi comparatiu de la publicació científica de la UPC i l'ETSETB vs. altres universitats d'àmbit europeu (1999 - 2009)

L'informe es centra en la publicació científica especialitzada en l'àmbit temàtic propi de l'ETSETB: l'enginyeria de telecomunicacións i l'electrònica. Es comparen indicadors bibliomètrics de la UPC i l'ETSETB amb els d'altres universitats europees amb activitat de recerca notable en l'àrea de les telecomunicacions i l'electrònica

Supervisory Adaptive Control Revisited: Linear-like Convolution Bounds

Classical feedback control for LTI systems enjoys many desirable properties including exponential stability, a bounded noise-gain, and tolerance to a degree of unmodeled dynamics. However, an accurate model for the system must be known. The field of adaptive control aims to allow one to control a system with a great deal of parametric uncertainty, but most such controllers do not exhibit those nice properties of an LTI system, and may not tolerate a time-varying plant. In this thesis, it is shown that an adaptive controller constructed via the machinery of Supervisory Control yields a closed-loop system which is exponentially stable, and where the effects of the exogenous inputs are bounded above by a linear convolution - this is a new result in the Supervisory Control literature. The consequences of this are that the system enjoys linear-like properties: it has a bounded noise-gain, is robust to a degree of unmodeled dynamics, and is tolerant of a degree of time-varying plant parameters. This is demonstrated in two cases: the first is the typical application of Supervisory Control - an integral control law is used to achieve step tracking in the presence of a constant disturbance. It is shown that the tracking error exponentially goes to zero when the disturbance is constant, and is bounded above by a linear convolution when it is not. The second case is a new application of Supervisory Control: it is shown that for a minimum phase plant, the d-step-ahead control law may be used to achieve asymptotic tracking of an arbitrary bounded reference signal. In addition to the convolution bound, a crisp bound is found on the 1-norm of the tracking error when a disturbance is absent

Stima con metodi subspace di parametri fisici in modelli differenziali alle derivate parziali

I metodi subspace sono algoritmi di algebra lineare per la stima dei parametri di modelli state-space a partire dai dati di ingresso e uscita del modello. Utilizzando come problema test il modello ottenuto dalla discretizzazione nel tempo e nello spazio dell'equazione del calore, in questa tesi si studia in particolar modo il problema di garantire la stabilita' del modello stimato dal metodo subspac

Control law and state estimators design for multi-agent system with reduction of communications by event-triggered approach

A large amount of research work has been recently dedicated to the study of Multi-Agent System and cooperative control. Applications to mobile robots, like unmanned air vehicles (UAVs), satellites, or aircraft have been tackled to insure complex mission such as exploration or surveillance. However, cooperative tasking requires communication between agents, and for a large number of agents, the number of communication exchanges may lead to network saturation, increased delays or loss of transferred packets, from the interest in reducing them. In event-triggered strategy, a communication is broadcast when a condition, based on chosen parameters and some threshold, is fulfilled. The main difficulty consists in determining the communication triggering condition (CTC) that will ensure the completion of the task assigned to the MAS. In a distributed strategy, each agent maintains an estimate value of others agents state to replace missing information due to limited communication. This thesis focuses on the development of distributed control laws and estimators for multi-agent system to limit the number of communication by using event-triggered strategy in the presence of perturbation with two main topics, i.e. consensus and formation control. The first part addresses the problem of distributed event-triggered communications for consensus of a multi-agent system with both general linear dynamics and state perturbations. To decrease the amount of required communications, an accurate estimator of the agent states is introduced, coupled with an estimator of the estimation error, and adaptation of communication protocol. By taking into account the control input of the agents, the proposed estimator allows to obtain a consensus with fewer communications than those obtained by a reference method. The second part proposes a strategy to reduce the number of communications for displacement-based formation control while following a desired reference trajectory. Agent dynamics are described by Euler-Lagrange models with perturbations and uncertainties on the model parameters. Several estimator structures are proposed to rebuilt missing information. The proposed distributed communication triggering condition accounts for inter-agent displacements and the relative discrepancy between actual and estimated agent states. A single a priori trajectory has to be evaluated to follow the desired path. Effect of state perturbations on the formation and on the communications are analyzed. Finally, the proposed methods have been adapted to consider packet dropouts and communication delays. For both type

Active vibration control of civil engineering structures

This thesis is in the area of active vibration control of Civil Engineering structures subject to earthquake loading. Existing structural control methods and technologies including passive, active, semi-active and hybrid control are first introduced. An extensive analysis of a frame-pendulum model is developed and analysed to investigate under what conditions effective energy dissipation is achieved in Tuned Mass Damper systems and the limitation of these devices under stiffness degradation when the structure enters the inelastic region. Linear Quadratic Gaussian and H-infinity active control schemes are designed, simulated and assessed for buildings, modelled as lumped parameter systems, including base and actuator dynamics. Various aspects of the designs are extensively evaluated using multiple criteria and loading conditions and validated in large-scale benchmark problems under practical limitations and implementation constraints. A novel design method is proposed for minimising peak responses of regulated signals via a deadbeat parametrisation of all stabilising controllers in discrete-time. The method incorporates constraints on the magnitude and rate of the control signal and is solved via efficient Linear Programming methods. It is argued that this type of optimisation is more relevant for structural control, as failure occurs when maximum member displacements are exceeded. The problem of stiffness matrix estimation from experimental data is formulated as an optimisation problem and solved under various conditions (positive definiteness, tridiagonal structure) via an alternating convex projection scheme. Both static and dynamic loading is considered. The method is finally incorporated in an adaptive control scheme involving the redesign in real-time of an LQR (Linear Quadratic Regulator) active vibration controller. It is shown that the method is successful in recovering the stability and performance properties of the nominal design under conditions of significant uncertainty in the stiffness parameters