http://hdl.handle.net/2117/2253 2013-05-20T00:56:42Z http://hdl.handle.net/2117/18424 Title: Application of predictive control strategies to the management of complex networks in the urban water cycle Authors: Ocampo-Martínez, Carlos; Puig Cayuela, Vicenç; Cembrano Gennari, Gabriela; Quevedo Casín, Joseba Jokin Abstract: The management of the urban water cycle (UWC) is a subject of increasing interest because of its social, economic, and environmental impact. The most important issues include the sustainable use of limited resources and the reliability of service to consumers with adequate quality and pressure levels, as well as the urban drainage management to prevent flooding and polluting discharges to the environment. 2013-03-19T18:02:56Z http://hdl.handle.net/2117/18378 Title: Stochastic exploration of ambiguities for nonrigid shape recovery Authors: Moreno-Noguer, Francesc; Fua, Pascal Abstract: Recovering the 3D shape of deformable surfaces from single images is known to be a highly ambiguous problem because many different shapes may have very similar projections. This is commonly addressed by restricting the set of possible shapes to linear combinations of deformation modes and by imposing additional geometric constraints. Unfortunately, because image measurements are noisy, such constraints do not always guarantee that the correct shape will be recovered. To overcome this limitation, we introduce a stochastic sampling approach to efficiently explore the set of solutions of an objective function based on point correspondences. This allows to propose a small set of ambiguous candidate 3D shapes and then use additional image information to choose the best one. As a proof of concept, we use either motion or shading cues to this end and show that we can handle a complex objective function without having to solve a difficult non-linear minimization problem. The advantages of our method are demonstrated on a variety of problems including both real and synthetic data. 2013-03-18T18:31:33Z http://hdl.handle.net/2117/17952 Title: Real-time segmentation of stereo videos on a portable system with a mobile GPU Authors: Abramov, Alexey; Pauwels, Karl; Papon, Jeremie; Wörgötter, Florentin; Dellen, Babette Abstract: In mobile robotic applications, visual information needs to be processed fast despite resource limitations of the mobile system. Here a novel real-time framework for model- free spatio-temporal segmentation of stereo videos is presented. It combines real-time optical flow and stereo with image seg- mentation and runs on a portable system with an integrated mobile GPU. The system performs on-line, automatic and dense segmentation of stereo videos and serves as a visual front- end for preprocessing in mobile robots, providing a condensed representation of the scene which can potentially be utilized in various applications, e.g., object manipulation, manipulation recognition, visual servoing. The method was tested on real-world sequences with arbitrary motions including videos acquired with a moving camera. 2013-02-22T16:58:21Z http://hdl.handle.net/2117/17693 Title: General robot kinematics decomposition without intermediate markers Authors: Ulbrich, Stefan; Ruiz de Angulo García, Vicente; Asfour, Tamim; Torras, Carme; Dillmann, Rüdiger Abstract: The calibration of serial manipulators with high numbers of degrees of freedom by means of machine learning is a complex and time-consuming task. With the help of a simple strategy, this complexity can be drastically reduced and the speed of the learning procedure can be increased: When the robot is virtually divided into shorter kinematic chains, these subchains can be learned separately and, hence, much more efficiently than the complete kinematics. Such decompositions, however, require either the possibility to capture the poses of all endeffectors of all subchains at the same time, or they are limited to robots that fulfill special constraints. In this work, an alternative decomposition is presented that does not suffer from these limitations. An offline training algorithm is provided in which the composite subchains are learned sequentially with dedicated movements. A second training scheme is provided to train composite chains simultaneously and online. Both schemes can be used together with many machine learning algorithms. In the simulations, an algorithm using Parameterized Self-Organizing Maps (PSOM) modified for online learning and Gaussian Mixture Models (GMM) were chosen to show the correctness of the approach. The experimental results show that, using a two-fold decomposition, the number of samples required to reach a given precision 2013-02-12T18:29:11Z http://hdl.handle.net/2117/17688 Title: Randomized path planning on manifolds based on higher-dimensional continuation Authors: Porta Pleite, Josep Maria; Jaillet, Leonard Georges; Bohigas Nadal, Oriol Abstract: Despite the significant advances in path planning methods, highly constrained problems are still challeng- ing. In some situations, the presence of constraints defines a configuration space that is a non-parametrizable manifold embedded in a high dimensional ambient space. In these cases, the use of sampling-based path planners is cumbersome since samples in the ambient space have low probability to lay on the configuration space manifold. In this paper, we present a new path planning algorithm specially tailored for highly constrained systems. The proposed planner builds on recently developed tools for higher-dimensional continuation, which provide numerical procedures to describe an implicitly defined manifold using a set of local charts. We propose to extend these methods focussing the generation of charts on the path between the two configurations to connect and randomizing the process to find alternative paths in the presence of obstacles. The advantage of this planner comes from the fact that it directly operates into the configuration space and not into the higher-dimensional ambient space, as most of the existing methods do. 2013-02-12T18:06:46Z http://hdl.handle.net/2117/17455 Title: Cooperative social robots to accompany groups of people Authors: Garrell Zulueta, Anais; Sanfeliu Cortés, Alberto Abstract: This study proposes a new model for guiding people in urban settings using multiple robots that work cooperatively. More speci cally, this investigation describes the circumstances in which people might stray from the formation when following di erent robots' instructions. To this end, we introduce a \Prediction and Anticipation Model" that predicts the position of the group using a Particle Filter, while determining the optimal robot behavior to help people stay in the group in areas where they may become distracted. As a result, this article presents a novel approach to locally optimizing the work performed by robots and people using the minimum robots' work criterion and determining humanfriendly types of movements. The guidance missions were carried out in urban areas that included multiple conflict areas and obstacles. This study also provides an analysis of robots' behavioral reactions to people by simulating di erent situations in the locations that were used for the investigation. The method was tested through simulations that took into account the di culties and technological constraints derived from real-life situations. Despites these problematic issues, we were able to demonstrate the robots' e ect on people in real-life situations in terms of pushing and dragging forces. 2013-01-21T17:42:48Z http://hdl.handle.net/2117/17452 Title: A personal account of Turing’s imprint on the development of computer science Authors: Díaz, Josep; Torras, Carme Abstract: The rst part of the XX century saw the development of the digital computer and the eld of computer science. In the present paper, we sketch our vision of that period and of the role that Alan Turing and some of his contemporary peers played in that development. 2013-01-21T17:23:25Z http://hdl.handle.net/2117/17431 Title: On the primal and dual forms of the Stewart platform pure condition Authors: Borràs Sol, Júlia; Thomas, Federico Abstract: The algebraic characterization of the singularities of a Stewart platform is usually presented as a 6 × 6 determinant, whose rows correspond to the line coordinates of its legs, equated to zero. This expression can be rewritten in a more amenable way, known as the pure condition, as sums and products of 4×4 determinants whose rows correspond to the point coordinates of the legs attachments. Researchers usually rely on one of these two expressions to find the geometric conditions associated with the singularities of a particular Stewart platform. Although both are equivalent, it is advantageous to use either line or point coordinates depending on the platform topology. In this context, an equivalent expression involving only plane coordinates, a dual expression to that using point coordinates, seems to be missing. This paper is devoted to its derivation and to show how its use is advantageous in many practical cases mainly because of its surprising simplicity: it only involves the addition of 4 × 4 determinants whose rows are plane coordinates defined by sets of three attachments. 2013-01-18T18:35:34Z http://hdl.handle.net/2117/17357 Title: Kinematic Bézier maps Authors: Ulbrich, Stefan; Ruiz de Angulo García, Vicente; Torras, Carme; Asfour, Tamim; Dillmann, Rudiger Abstract: The kinematics of a robot with many degrees of freedom is a very complex function. Learning this function for a large workspace with a good precision requires a huge number of training samples, i.e., robot movements. In this paper, we introduce the Kinematic Bézier Map (KB-Map), a parameterizable model without the generality of other systems but whose structure readily incorporates some of the geometric constraints of a kinematic function. In this way, the number of training samples required is drastically reduced. Moreover, the simplicity of the model reduces learning to solving a linear least squares problem. Systematic experiments have been carried out showing the excellent interpolation and extrapolation capabilities of KB-Maps and their relatively low sensitivity to noise. 2013-01-14T18:06:08Z http://hdl.handle.net/2117/17230 Title: Direct synchronous-asynchronous conversion system for hybrid electrical vehicle applications. An energy-based modeling approach Authors: Muñoz Aguilar, Raúl Santiago; Dòria Cerezo, Arnau; Puleston, Paul Abstract: This paper presents a proposal for a series hybrid electric vehicle propulsion system. This new configuration is based on a wound-rotor synchronous generator (WRSM) and a doubly-fed induction machine (DFIM). The energy-based model of the whole system is obtained taking advantage of the capabilities of the port-based modeling techniques. From the dq port-controlled Hamiltonian description of the WRSM and DFIM, the Hamiltonian model of the proposed Direct Synchronous-Asynchronous Conversion System (DiSAC) is developed. Subsequently, the bond graph models of the DiSAC and associate systems are also provided. Numerical simulations are also presented in order to validate the proposed system 2013-01-09T11:36:16Z http://hdl.handle.net/2117/17219 Title: A linear relaxation method for computing workspace slices of the Stewart platform Authors: Bohigas Nadal, Oriol; Manubens Ferriol, Montserrat; Ros Giralt, Lluís Abstract: The workspace of a Stewart platform is a complex sixdimensional volume embedded in the Cartesian space defined by six pose parameters. Because of its large dimension and complex shape, this volume is difficult to compute and represent, and comprehension on its structure is being gained by studying its three-dimensional slices. While successful methods have been given to determine the constantorientation slice, the computation and appropriate visualization of the constant-position slice (also known as the orientation workspace) has proved to be a challenging task. This paper presents a unified method for computing both of such slices, and any other ones defined by fixing three pose parameters, on general Stewart platforms possibly involving mechanical limits on the active and passive joints. Advantages over existing methods include, in addition to the previous, the ability to determine all connected components of the workspace, and any motion barriers present in its interior. 2013-01-08T17:35:44Z http://hdl.handle.net/2117/17218 Title: Exploring the energy landscapes of flexible molecular loops using higher-dimensional continuation Authors: Porta Pleite, Josep Maria; Jaillet, Leonard Georges Abstract: The conformational space of a flexible molecular loop includes the set of conformations fulfilling the geometric loop-closure constraints and its energy landscape can be seen as a scalar field defined on this implicit set. Higher-dimensional continuation tools, recently developed in Dynamical Systems and also applied to Robotics, provide efficient algorithms to trace out implicitly defined sets. This paper describes these tools and applies them to obtain full descriptions of the energy landscapes of short molecular loops that, otherwise, can only be partially explored, mainly via sampling. Moreover, to deal with larger loops, this paper exploits the higher-dimensional continuation tools to find local minima and minimum energy transition paths between them, without deviating from the loop-closure constraints. The proposed techniques are applied to previously studied molecules revealing the intricate structure of their energy landscapes. 2013-01-08T17:17:30Z http://hdl.handle.net/2117/15792 Title: Experimental characterization methodology for the identification of voltage losses of PEMFC: applied to an open cathode stack Authors: Husar, Attila Peter; Strahl, Stephan; Riera Colomer, Jordi Abstract: The objective of this study is to describe the methodology used to isolate the main voltage loss indicators through a simple and effective treatment of a current interrupt and current sweep. The voltage loss indicators are activation polarization, mass transport, and ohmic losses. The indicators for these losses are the Tafel slope, mass transport resistance and ohmic resistance respectively. The use of this methodology to isolate the individual voltage losses works quite well. Even though there may be some inaccuracies, the trends can be clearly seen. This methodology can be used in any PEMFC system to monitor the state of health of the fuel cell. If this method were to be automated and implemented on a periodic basis, then an on-line measurement of the individual voltage losses could be monitored. The data analysis indicates that a major objective of the controller will be to minimize the mass transport losses by implementing proper temperature control. 2012-05-07T17:47:45Z http://hdl.handle.net/2117/15791 Title: A comprehensive dynamic model for class-1 tensegrity systems based on quaternions Authors: Cefalo, Massimo; Mirats Tur, Josep Maria Abstract: In this paper we propose a new dynamic model, based on quaternions, for tensegrity systems of class-1. Quaternions are used to represent orientations of a rigid body in the 3-dimensional space eliminating the problem of singularities. Moreover, the equations based on quaternions allow to perform more precise calculations and simulations because they do not use trigonometric functions for the representation of angles. We present a thorough introduction of tensegrities and the current state of research. We also introduce the quaternions and provide in the appendix some important details and useful properties. Applying the Euler–Lagrange approach we derive a comprehensive dynamic model, first for a simple rigid bar in the space and, at last, for a class-1 tensegrity system. We present two model forms: a matrix and a vectorial form. The first more compact and easier to write, the latter more suitable to apply the tools and the theory based on vector fields. 2012-05-07T17:42:01Z http://hdl.handle.net/2117/15790 Title: A generic framework for median graph computation based on a recursive embedding approach Authors: Ferrer Sumsi, Miquel; Karatzas, D; Valveny, Ernest; Bardaji Goikoetxea, Itziar; Bunke, Horst Abstract: The median graph has been shown to be a good choice to obtain a representative of a set of graphs. However, its computation is a complex problem. Recently, graph embedding into vector spaces has been proposed to obtain approximations of the median graph. The problem with such an approach is how to go from a point in the vector space back to a graph in the graph space. The main contribution of this paper is the generalization of this previous method, proposing a generic recursive procedure that permits to recover the graph corresponding to a point in the vector space, introducing only the amount of approximation inherent to the use of graph matching algorithms. In order to evaluate the proposed method, we compare it with the set median and with the other state-of-the-art embedding-based methods for the median graph computation. The experiments are carried out using four different databases (one semi-artificial and three containing real-world data). Results show that with the proposed approach we can obtain better medians, in terms of the sum of distances to the training graphs, than with the previous existing methods. 2012-05-07T17:30:35Z