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In this paper we propose a new control-oriented design technique to enhance the algorithmic performance of the distributed gradient tracking algorithm. We focus on a scenario in which agents in a network aim to cooperatively minimize the sum of convex, quadratic cost functions depending on a common decision variable. By leveraging a recent system-theoretical reinterpretation of the considered algorithmic framework as a closed-loop linear dynamical system, the proposed approach generalizes the diagonal gain structure associated to the existing gradient tracking algorithms. Specifically, we look for closed-loop gain matrices that satisfy the sparsity constraints imposed by the network topology, without however being necessarily diagonal, as in existing gradient tracking schemes. We propose a novel procedure to compute stabilizing sparse gain matrices by solving a set of nonlinear matrix inequalities, based on the solution of a sequence of approximate linear versions of such inequalities. Numerical simulations are presented showing the enhanced performance of the proposed design compared to existing gradient tracking algorithms.

Objectives: To evaluate the exposure of Portuguese Urology residents (IP) to urological laparoscopy and to its training methods, comparing with the remaining Urology residents in Europe (IE).Materials and methods: A survey consisting of 23 questions concerning laparoscopic training, which was published online as well as distributed on paper, during the Annual European. Association of Urology Congress in 2012. Data was analysed with descriptive statistics, student t, Mann-Whitney and χ2 tests.Results: We obtained 219 valid responses, 53 (24.2%) of which from IP. Conventional laparoscopy is equally available for both groups (78.8% of IP vs 72.0% of IE, p = NS). IP have greater access to single port laparoscopy (22.6% vs 8.4%, p < 0.05), but lesser exposure to robot-assisted laparoscopy (0% vs 21.9%, p < 0.01) in their training departments. Performance of conventional laparoscopy as first surgeons was reported by 32.7% of IP and 24.8% of IE (p = NS). The most commonly performed procedure was total nephrectomy (38.4% of IP and 28.8% of IE, p = NS). The majority in both groups considered their laparoscopic experience at the moment of the survey to be “Poor” or worse (81.9% of IP e 75.5% of IE, p = NS). However, IP had greater expectations than IE of improvement during residency (p = 0.01). No previous attendance to laparoscopic courses or fellowships was seen in 35.7% of IP and 41.7% of IE (p = NS). However, IP attended more national courses than IE. “Pelvitrainer” is the most commonly available laboratory training method, (30.2% of IP and 33.3% of IE, p = NS), but 41.9% of IP and 42.4% IE do not have access to any laparoscopic training device. Most residents (84.1% of IP and 74.4% of IE, p = NS) rate their motivation to perform laparoscopy in the future as “High” or “Very High”, and plan performing a post-residency fellowship in this field.Conclusions: The access to conventional laparoscopy is similar between IP and IE, and both take an active part in this technique. A significant proportion has some experience as laparoscopic surgeons. Despite the relative scarcity of training devices in both groups, IP attend more national courses in laparoscopy, and experience a better sense of evolution during residency than IE.© 2014 Associação Portuguesa de Urologia. Published by Elsevier España, S.L.U. All rights reserved.

This paper deals with the problem of modelling and controlling a vertical take-off and landing aircraft equipped with a lightweight robotic arm. This system is able to perform complex operations that require the physical interaction with the environment while remaining airborne. Once the dynamical model in the 3D case is provided, a control law able to let the degrees of freedom of the system to track a desired trajectory is derived. The proposed controller takes into account the interaction between the robotic arm and the aerial platform both during free-flight and in the presence of unknown contact forces deriving from the interaction with the environment. The effectiveness and main properties of the proposed control algorithm have been analytically investigated and then demonstrated with the help of an experiment.

In this paper, an averaging control strategy is proposed for the DC link voltage dynamics of shunt active filters (SAF), which are used in three-phases current harmonic compensation. The SAF considered are based on AC/DC three-phase boost converter topology. Power losses due to parasitic resistances cause the instability of the voltage dynamics. The robust solution for perfect harmonics compensation, presented by Marconi et la. (2004) is used, while the dead zone voltage controller from these previous works is replaced by a new one that directly stabilizes the average value of the voltage, allowing for the necessary voltage oscillations during operation, and improving the voltage dynamics behavior. The average component is calculated directly from measurement of the actual voltage, using the so-called phasors method. A standard PI controller, which is designed in the frame of averaged values, is used for stabilization. Some additional work is required to obtain the actual control input based on the averaged values delivered by the controller

In this paper we study the problem of information disclosure in ontology-based data access (OBDA). Following previous work on Controlled Query Evaluation, we introduce the framework of Policy-Protected OBDA (PPOBDA), which extends OBDA with data protection policies specified over the ontology and enforced through a censor, i.e., a function that alters answers to users’ queries to avoid the disclosure of protected data. We consider PPOBDA systems in which the ontology is expressed in \(\textsc {owl\,2\,ql} \) and the policies are denial constraints, and show that query answering under censors in such a setting can be reduced to standard query answering in OBDA (without data protection policies). The basic idea of our approach is to compile the policies of a PPOBDA system into the mapping of a standard OBDA system. To this aim, we analyze some notions of censor proposed in the literature, show that they are not suited for the above-mentioned compilation, and provide a new definition of censor that enables the effective realization of our idea. We have implemented our technique and evaluated it over the NPD benchmark for OBDA. Our results are very promising and show that controlled query evaluation in OBDA can be realized in the practice by using off-the-shelf OBDA engines.

This work proposes a feedback control strategy to let the dynamics of an under-actuated Vertical Take-Off and Landing (VTOL) aerial vehicle to track a desired trajectory thanks to an adaptive robust compensation of the aerodynamic disturbances. The novelty of the proposed approach consists in employing an aerodynamic disturbance observer derived using the NonLinear Geometric Approach and Radial Basis Functions (RBF). The obtained estimation is directly employed by a nonlinear robust feedback law which relies on a cascade control paradigm in which the attitude dynamics and the position dynamics of the vehicle play the role of the inner and of the outer loop, respectively. The robustness of the proposed approach is also demonstrated by means of simulation results in which the aerodynamic model of a multi-propeller aircraft is considered.

International audience

CF '16 Proceedings of the ACM International Conference on Computing Frontiers, ISBN:978-1-4503-4128-8

This work focuses on the modeling and control of an innovative configuration of aerial robot arising from the combination of a vertical take-off and landing aircraft and a robotic arm. The overall system, denoted as aerial manipulator, is able to accomplish operations requiring the physical interaction with the surrounding environment while remaining airborne. After introducing a detailed dynamical model, a control law, based on the impedance control paradigm, able to govern all the degrees of freedom of the system is proposed. The effectiveness of the proposed control algorithm are investigated also considering the case in which contacts with the surrounding environment are achieved.

In this paper an advanced control strategy is proposed for shunt active filter (SAF) used in three-phases three-wires current harmonic compensation. The SAF considered are based on AC/DC three-phase boost converter topology. The robust solution presented by the authors previously is used as a starting point to develop the stabilizing controller of the DC-MA voltage dynamics. SAF resistive power losses cause the instability of this voltage dynamics when perfect harmonics compensation is achieved. An integrator with a suitably designed deadzone is placed in the voltage controller to guarantee DC-link voltage dynamics stabilization without perturbing the current harmonics compensation. Two time-scale behavior of the SAF is exploited to apply the averaging technique and input to state stability arguments in the control design.

This paper deals with the problem of adaptive output regulation for linear multivariable systems. The proposed solution employs a continuous-time identifier that adapts the parameters of the internal model to match the (unknown) exosystem frequencies. Boundedness of the closed-loop trajectories is established and, under a persistence of excitation condition, asymptotic regulation is shown.

We consider the problem of output feedback robust stabilization of a ducted-fan aerial vehicle in which high-gain observers are used to overtake the knowledge of the linear and angular velocities of the vehicle in the control law. The proposed result is semiglobal in the attitude dynamics and in the estimation error, and global in the position variables. It is shown how the high-gain control structure is effective notwithstanding the nonminimum-phase behavior of the considered class of systems, provided that the airframe fulfills some geometric properties. The controller relies upon the use of nested saturations and high-gain control laws. Although the theory is specified for a force-torque generation mechanism of a ducted-fan aerial vehicle, the results can be simply extended to the output feedback of many other under-actuated rotorcrafts, such as helicopters. Experimental results are also proposed showing the effectiveness of the control law. We consider the problem of output feedback robust stabilization of a ducted-fan aerial vehicle in which high-gain observers are used to overtake the knowledge of the linear and angular velocities of the vehicle in the control law. The proposed result is semiglobal in the attitude dynamics and in the estimation error, and global in the position variables. It is shown how the high-gain control structure is effective notwithstanding the nonminimum-phase behavior of the considered class of systems, provided that the airframe fulfills some geometric properties. The controller relies upon the use of nested saturations and high-gain control laws. Although the theory is specified for a force-torque generation mechanism of a ducted-fan aerial vehicle, the results can be simply extended to the output feedback of many other under-actuated rotorcrafts, such as helicopters. Experimental results are also proposed showing the effectiveness of the control law.

We present a dynamical model for the double torsion pendulum nicknamed PETER, where one torsion pendulum hangs in cascade, but off-axis, from the other. The dynamics of interest in these devices lies around the torsional resonance, that is at very low frequencies (mHz). However, we find that, in order to properly describe the forced motion of the pendulums, also other modes must be considered, namely swinging and bouncing oscillations of the two suspended masses, that resonate at higher frequencies (Hz). Although the system has obviously 6+6 Degrees of Freedom, we find that 8 are sufficient for an accurate description of the observed motion. This model produces reliable estimates of the response to generic external disturbances and actuating forces or torques. In particular, we compute the effect of seismic floor motion (tilt noise) on the low frequency part of the signal spectra and show that it properly accounts for most of the measured low frequency noise., 15 pages, 6 figures

In this paper we present a novel internal model-based control method for hysteresis compensation. A hybrid model is proposed for characterization of the hysteresis nonlinearity of the well-known play operator (Backlash). The proposed model holds the hysteresis nonlinearity and the memory effects of the play operator. Based on the proposed model, a hybrid controller is designed to compensate for the hysteresis nonlinearity of the play operator. Following an internal model approach, the hybrid controller integrates a hybrid integrator dynamics which is able to estimate asymptotically the unknown value of the threshold characterizing the hysteresis and hence to obtain perfect tracking of a periodic reference signal. Simulation results are also presented to show the capability of the hybrid model to present the hysteresis nonlinearity with memory effects, and the effectiveness of proposed hybrid controller to compensate for the uncertain hysteresis nonlinearity.

International audience; This paper presents a nonlinear canonical form which is used for the design of a reduced order observer. Sufficient and necessary geometric conditions are given in order to transform a special class of nonlinear systems to the proposed nonlinear canonical form and the corresponding reduced order observer is analyzed.