Publications

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Authors: Smith, AG;

Journal: English

Published: title_year

DOI: WOS:000265844200013

Pages: 188-Information Access through Search Engines and Digital Libraries

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Authors: Pretto, I; Ruffieux, S; Menon, C; Ijspeert, AJ; Cocuzza, S; Sch Engn Sci; Sch Engn Sci; Biol Inspired Res Grp; CISAS G Colombo Ctr Studies & Activ Space; Bio-inspired climbing robots relying on adhesion systems are believed to become essential tools for several industrial applications in the near future. In recent years, research has mainly focused on modeling micro-scale adhesion phenomena; a macro-scale adhesion model has however to be developed for the design of macro-scale systems. In this paper a macro-model of adhesion suitable for real-time applications is presented; it relies on a continuous representation of adhesion. An extension of the von Mises criterion is proposed as failure adhesion criterion in order to estimate the occurrence of detachment at any point of the contacting surface. An experimental set up has been designed in order to define the parameters of the model. A semi-automatic process has been developed to ensure repeatability and accuracy of the results. Polydimethylsiloxane (PDMS), which has revealed promising adhesive features for robotic use, has been used during the experimental phase. The macro-model of adhesion has been implemented in a multi-body dynamics environment based on Open Dynamics Engine (ODE) to simulate a spider-inspired robot. Simulations based on this model are suitable to represent the behaviour of climbing robots and also to optimize their design. © 2008 Jilin University. Pretto; Ruffieux; Menon; Ijspeert; Cocuzza

Journal: English

Published: doi

DOI: WOS:000260115200017

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Volume: JOURNAL OF BIONIC ENGINEERING###1672-6529 Pages: 105-A Point-Wise Model of Adhesion Suitable for Real-Time Applications of Bio-Inspired Climbing Robots

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Authors: Peserico, E; Pretto, L; Dip Ing Informaz; Dip Ing Informaz; This paper explores the fundamental question of how many iterations the celebrated HITS algorithm requires on a general graph to converge in score and, perhaps more importantly, in rank (i.e. to "get right" the order of the nodes). We prove upper and almost matching lower bounds. We also extend our results to weighted graphs. © 2009 Springer Berlin Heidelberg. Peserico; Pretto

Journal: English

Published: doi

DOI: WOS:000269148100035

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Pages: 357-HITS Can Converge Slowly, but Not Too Slowly, in Score and Rank

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Authors: Peserico, E; Pretto, L; Dip Ing Informaz; Dip Ing Informaz; How many iterations does the (ever more) popular HITS algorithm require to converge in score and, perhaps more importantly, in rank (i.e. to get the nodes of a graph "in the right order")? After pinning down the elusive notion of convergence in rank we provide the first non-trivial bounds on the convergence of HITS. A "worst case" example, requiring a number of iterations superexponential in the size of the target graph to achieve even "mild" convergence, suggests the need for greater caution in the experimental evaluation of the algorithm - as recent results of poor performance (e.g. vs. SALSA) might be due to insufficient iterations, rather than to an intrinsic deficiency of HITS. An almost matching upper bound shows that, as long as one employs exponential acceleration e.g. through a "squaring trick", a polynomial running time (practical in many application domains) always provides strong convergence guarantees. Peserico; Pretto

Journal: English

Published: doi

DOI: WOS:000270976500152

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Pages: 771-Score and Rank Convergence of HITS

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Authors: AREA MIN. 07 - Scienze agrarie e veterinarie

Published: title_year

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Authors: Celesti-Grapow, L; Alessandrini, A; Arrigoni, PV; Banfi, E; Bernardo, L; Bovio, M; Brundu, G; Cagiotti, MR; Camarda, I; Carli, E; Conti, F; Fascetti, S; Galasso, G; Gubellini, L; La Valva, V; Lucchese, F; Marchiori, S; Mazzola, P; Peccenini, S; Poldini, L; Pretto, F; Prosser, F; Siniscalco, C; Villani, MC; Viegi, L; Wilhalm, T; Blasi, C; Dept Plant Biol; Dept Plant Biol; Bot Garden; Dept Bot & Plant Ecol; Dept Appl Biol; Dept Environm Sci; Dept Biol; Landscape Study Dept; In this paper we present a comprehensive inventory of the non-native vascular flora of Italy, which was produced within the project "A survey of the Italian non-native flora", funded by the Italian Ministry for the Environment. Previously published floristic accounts were the main source of information. Historical records were critically revised and integrated with recent literature, data from herbaria and some unpublished information, so as to obtain a complete, up-to-date catalogue of the non-native vascular plant species that occur spontaneously in Italy. The inventory lists 1023 non-native species and subspecies, which account for 13.4% of all the Italian flora. The Italian non-native flora was divided, according to its residence time, into 103 archaeophytes and 920 neophytes. According to its current invasion status, it was classified into 437 casual (42.7% of all non-native) and 524 established taxa, the latter being divided into 361 naturalized non-invasive (35.3%) and 163 invasive taxa (15.9%). The inventory includes a group of 62 species (6.1%) that lack recent records (i.e. since 1950). By combining local expertise into a unified, nationwide scheme using a standardized method and terminology, the inventory provides the essential scientific basis for the development of plant invasion research and management in the country. © 2009 Società Botanica Italiana. Celesti-Grapow; Alessandrini; Arrigoni; Banfi; Bernardo; Bovio; Brundu; Cagiotti; Camarda; Carli; Conti; Fascetti; Galasso; Gubellini; la Valva; Lucchese; Marchiori; Mazzola; Peccenini; Poldini; Pretto; Prosser; Siniscalco; Villani; Viegi; Wilhalm; Blasi

Journal: English

Published: doi

DOI: WOS:000272170900017

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Volume: PLANT BIOSYSTEMS###1126-3504 Pages: 430-Inventory of the non-native flora of Italy

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Authors: AREA MIN. 07 - Scienze agrarie e veterinarie

Published: title_year

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Authors: Cocuzza, S; Pretto, I; Debei, S; CISAS G Colombo; CISAS G Colombo; Dept Mech Engn; This paper presents two novel redundancy resolution schemes aimed at locally minimizing the reaction torque transferred to the spacecraft during manipulator manoeuvres. The subject is of particular interest in space robotics because reduced reactions result in reduced energy consumption and longer operating life of the attitude control system. The first presented solution is based on a weighted Jacobian pseudoinverse and is derived by using Lagrangian multipliers. The weight matrix is defined by means of the inertia matrix which appears in the spacecraft reaction torque dynamics. The second one is based on a least squares formulation of the minimization problem. In this formulation the linearity of the forward kinematics and of the reaction torque dynamics equations with respect to the joint accelerations is used. A closed-form solution is derived for both the presented methods, and their equivalence is proven analytically. Moreover, the proposed solutions, which are suitable for real-time implementation, are extended in order to take into account the physical limits of the manipulator joints directly inside the solution algorithm. A software simulator has been developed in order to simulate the performance of the presented solutions for the selected test cases. The proposed solutions have then been experimentally tested using a 3D free-flying robot previously tested in an ESA Parabolic Flight Campaign. In the test campaign the 3D robot has been converted in a 2D robot thanks to its modularity in order to perform planar tests, in which the microgravity environment can be simulated without time constraints. Air-bearings are used to sustain the links weight, and a dynamometer is used to measure the reaction torque. The experimental validation of the presented inverse kinematics solutions, with an insight on the effect of joint flexibility on their performance, has been carried out, and the experimental results confirmed the good performance of the proposed methods. In particular, two test cases have been analyzed in order to validate and evaluate the performance of both the unconstrained solution and the solution which takes into account the robot physical limits. Cocuzza; Pretto; Debei

Journal: English

Published: Cocuzza S.; Pretto I.; Debei S.

DOI: WOS:000291173900009

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Pages: 1721-Novel reaction control techniques for redundant space manipulators: Theory and simulated microgravity tests

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Authors: This paper presents the analysis and validation of a Least Squares based Inverse Kinematics solution for the control of the reaction torque transferred to the floating base of a redundant space manipulator. The solution, which is suitable for real-time implementation and can be extended in order to take into account the joint angle, velocity and acceleration limits, has been recently developed and experimentally validated by the authors in the case of a fixed-based planar manipulator. In this study, the solution is validated in the case of a planar three degrees of freedom free-floating manipulator by using a software simulator. Moreover, the operations of a free-floating robot and of a fixed-based robot are compared in different ways. First, the possibility to use fixed-based kinematic and dynamic models in order to reduce the computations necessary for the proposed solution is investigated. In particular, a limit base/arm mass ratio is derived, for which the approximated model can be favourably used, taking into account the requirements on base attitude pointing accuracy and end-effector trajectory accuracy. Then, the requirements on the maximum joint variables of a free-floating and of a fixed-based robot are compared for a given task. Higher joint angles, velocities and accelerations are expected with respect to a fixed-based robot that performs the same task, due to the base rotation displacements. This effect can be limited thanks to the proposed torque minimization solution, since motions can be studied in which a fixed base orientation is maintained, if sufficient redundant degrees of freedom are present. Finally, the study of the workspace in which a zero reaction torque can be obtained is performed for different base/arm mass ratios, both taking into account the physical joint limits or not. Cocuzza; Pretto; Debei

Journal: 2009

Published: Cocuzza S.; Pretto I.; Debei S.

DOI: 359006029

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Authors: AREA MIN. 09 - Ingegneria industriale e dell'informazione; ITA

Published: title_year