76 research outputs found
A Two-Stage Trajectory Optimization Strategy for Articulated Bodies with Unscheduled Contact Sequences
No full textIn this letter, we propose a two-stage strategy for optimal control problems of robotic mechanical systems that proves to be more robust, and yet more efficient, than straightforward solution strategies. Specifically, we focus on a simplified humanoid model, represented as a two-dimensional articulated serial chain of rigid bodies, in the tasks of getting up (sitting down) from (to) the supine and prone postures. Interactions with the environment are integral parts of these motions, and a priori unscheduled contact sequences are discovered by the solver itself, opportunistically making or breaking contacts with the ground through feet, knees, hips, elbows, and hands. The present investigation analyzes the effects on the computational performance of: 1) the explicit introduction of contact forces among the optimization variables, 2) the substitution of undesired contact forces with geometric constraints that prevent interpenetrations, and 3) the splitting of the planning problem into two consecutive phases of increasing complexity. To the best of our knowledge, these tests represent the only quantitative analysis of the performances achievable with different solution strategies for optimization-based, whole-body dynamic motion planning in the presence of contacts
Approximate hybrid model predictive control for multi-contact push recovery in complex environments
No full textFeedback control of robotic systems interacting with the environment through contacts is a central topic in legged robotics. One of the main challenges posed by this problem is the choice of a model sufficiently complex to capture the discontinuous nature of the dynamics but simple enough to allow online computations. Linear models have proved to be the most effective and reliable choice for smooth systems; we believe that piecewise affine (PWA) models represent their natural extension when contact phenomena occur. Discrete-time PWA systems have been deeply analyzed in the field of hybrid Model Predictive Control (MPC), but the straightforward application of MPC techniques to complex systems, such as a humanoid
robot, leads to mixed-integer optimization problems which are not solvable at real-time rates. Explicit MPC methods can
construct the entire control policy offline, but the resulting policy becomes too complex to compute for systems at the scale of a humanoid robot. In this paper we propose a novel algorithm which splits the computational burden between an offline sampling phase and a limited number of online convex optimizations, enabling the application of hybrid predictive controllers to higher-dimensional systems. In doing so we are willing to partially sacrifice feedback optimality, but we set stability of the system as an inviolable requirement. Simulation results of a simple planar humanoid that balances by making contact with its environment are presented to validate the proposed controller
Towards minimum-information adaptive controllers for robot manipulators
No full textThe aim of this paper is to move a step in the direction of determining the minimum amount of information needed to control a robot manipulator within the framework of adaptive control. Recent innovations in the state of the art show how global asymptotic trajectory tracking can be achieved despite the presence of uncertainties in the kinematic and dynamic models of the robot. However, a clear distinction between which parameters can be included among the uncertainties, and which parameters can not, has not been drawn yet. Since most of the adaptive control algorithms are built on linearly parameterized models, we propose to reformulate the problem as finding a procedure to determine whether and how a given dynamical system can be linearly parameterized with respect to a specific set of parameters. Within this framework, we show how the trajectory tracking problem of a manipulator can be accomplished with the only knowledge of the number of joints of the manipulator. As an illustrative example, we present the end-effector trajectory tracking control of a robot initialized with the kinematic model of a different robot
Domestication process of two Solanum (section Lasiocarpa) species among Amerindians in the Upper Orinoco, Venezuela with special focus on Piaroa indians
No full textVolpato, Gabriele, Rossella Marcucci, Noemi Tornadore, and Maurizio G. Paoletti (Department
of Biology, University of Padua, 325100 Padova, Italy; email corresponding author:
[email protected]). DOMESTICATION PROCESS OF TWO SOLANUM SECTION LASIOCARPA SPECIES
AMONG AMERINDIANS IN THE UPPER ORINOCO, VENEZUELA, WITH SPECIAL FOCUS ON PIAROA
INDIANS. Economic Botany 58(2):000–000, 2004. Two semi-cultivated Solanum species (S. sessiliflorum
Dunal and S. stramonifolium Jacq.) are utilized by the Amazonian Indians of the
Upper Orinoco Basin in Venezuela. The manner by which they have become partially domesticated
by the Piaroas and other native tribes of this rain forest region is elucidated in the
following text. Both species have two varieties, with and without prickles, the latter the result
of human selection. Patterns of indigenous utilization of these species by the selection of morphologic
forms and to the differentiation of karyotypes of varieties, and exploitation of the
species reflects also in the perception of them among users. S. sessiliflorum is cultivated in
swiddens and has an economic role, whereas S. stramonifolium is grown in dooryards. This
difference is detectable to the Piaroas, as they recognize in their folk taxonomy three different
varieties of the S. sessiliflorum and one of S. stramonifolium, this according to the stage of
domestication of the species and the way in which they are utilized
Vincoli intertestuali-intersemiotici in Naked People di A. Astvacaturov. Analisi, percezione, scelte traduttive
No full textThis study aims to continue research on cinema “intexts” (Torop 1995, It. Transl. 2010, also known as crossmedial relations (Fateeva 2007)) in Russian contemporary literture, focusing on their translation and underlining the primary importance of their analysis and function in the source text. The current research develops from previous work centered on cinema intertextuality in M. Elizarov’s novel Cartoons (Marcucci 2015a) and, secondarily, in E. Popov’s Internet novel Arbeit. A broad canvas (Marcucci 2015b). The current study follows up on this research by investigating Andrey Astvatsaturov’s novel Naked People (translated by the author) and pursuing three aims. 1. Analyze the types of intexts (which films does the author refer to? From which period? Of wich genres?) and the strategies used by the author to insert in his text references to other texts belonging to the cinema semiotic system, in which iconic signs have a primary role. 2. Explore the functions of these intexts. 3. Reflect on the operations to carry out when such texts are translated into a different linguacultural universe, specifically the Italian one. Here, the main focus will shift onto the translator’s role and task.
Parametric Trajectory Libraries for Online Motion Planning with Application to Soft Robots
No full textIn this paper we propose a method for online motion planning of constrained nonlinear systems. The method consists of three steps: the offline generation of a library of parametric trajectories via direct trajectory optimization, the online search in the library for the best candidate solution to the optimal control problem we aim to solve, and the online refinement of this trajectory. The last phase of this process takes advantage of a sensitivity-like analysis and guarantees to comply with the first-order approximation of the constraints even in case of active set changes. Efficiency of the trajectory generation process is discussed and a valid strategy to minimize online computations is proposed; together with this, an effective procedure for searching the candidate trajectory is also presented. As a case study, we examine optimal control of a planar soft manipulator performing a pick-and-place task: through simulations and experiments, we show how crucial online computation times are to achieve considerable energy savings in the presence of variability of the task to perform
Ponzio, Orazio Censore, Montano, Rainaldi per la cappella Colonna in S. Giovanni in Laterano
No full textLa cappella del coro d'inverno venne costruita nell'ambito della ristrutturazione della "nave trasversa" di S. Giovanni in Laterano patrocinata da Clemente VIII (Aldobrandini, 1592-1605), intrapresa appena dopo l'elezione al pontificato. Introdotta, dal deambulatorio – poi demolito – attraverso la sagrestia dei Beneficiati, già costruita nel 1594, anche la cappella del coro d'inverno, poi anche dei Colonna, deve risalire a quegli anni. E' attribuita, in base alle parole di antichi biografi e all'analisi critica di F. Fasolo, a Girolamo Rainaldi e l'esecuzione viene ricondotta agli anni del gran contestabile del Regno di Napoli Filippo Colonna che la ebbe nuovamente in assegnazione nel 1623 per costruirvi il monumento funebre della moglie Lucrezia Tomacelli, morta l'anno prima.
La documentazione edita e quella inedita rintracciata ha dimostrato che le vicende costruttive e decorative della cappella sono state lunghe e complesse, vedendo impegnati più artisti; lo "stile" di Rainaldi riconosciuto da Fasolo è in realtà comune anche ad altri artisti attivi negli stessi anni o poco prima, come Flaminio Ponzio, ricordato quale architetto della basilica nel 1597 in una annotazione di G. Zander e redattore di una stima sui lavori eseguiti nella cappella del 1613, dalla quale si sa che l'opera architettonica e decorativa era in quell’anno in gran parte eseguita.
Alla cultura di maestranze dell’entourage di Montano si è attribuito il progetto del coro ligneo per i canonici, di cui si è scritto nel commento al saggio precedente; Orazio Censore, noto fonditore di metalli, è richiamato da Baglione come autore della cappella – ma probabilmente solo per le numerose opere bronzee che la decorano -; Girolamo Rainaldi fu probabilmente solo l'autore della fase finale di completamento di opere impostate da altri, ma che hanno indotto la storiografia ad individuare e ricercare uno "stile" rainaldesco in più architetture del periodo.
The winter choir chapel was built within restoration of the “transverse nave" of the Basilica of St. John Lateran sponsored by Clement VIII (Aldobrandini, 1592-1605), which he started as soon as he became Pope. Connected through the ambulatory – then demolished – to the Sacristy of the Beneficiaries, already built in 1594, the winter choir chapel – named also the Colonna chapel later on – must date back to those years, too. In accordance with old biographers and the critical analysis of F. Fasolo, it was ascribed to Girolamo Rainaldi while the erection was related to the years of the Grand Constable of the Kingdom of Naples Filippo Colonna, to whom it was assigned again in 1623 for building in there a memorial of his wife Lucrezia Tomacelli, dying the year before.
Pursuant to both the published and unpublished documentation found, the construction and decoration aspects of the chapel were long and complex, with several artists at work; the "style" of Rainaldi, recognised by Fasolo, was in fact shared by other artists operating in those years or a little earlier, too, such as Flaminio Ponzio, mentioned as architect of the Basilica in 1597 in a note by G. Zander, and author of a survey on the works carried out at the chapel in 1613, through which it is known that the architectonic and decorative work was almost finished in that year.
The project of the wooden choir for canons was assigned to the workers from the Montano entourage; that project was mentioned in the commentary to the previous essay; Orazio Censore, well-known caster of metals is recalled by Baglione as the creator of the chapel, probably just for the numerous bronze works decorating it; Girolamo Rainaldi is likely to have carried out just the final phase, the completion of works planned by others, nevertheless inducing historiographers to identify or look for the Rainaldi style in several architectures of the period
Graphs of Convex Sets with Applications to Optimal Control and Motion Planning
No full textThis thesis introduces a new class of problems at the interface of combinatorial and convex optimization. We consider graphs where each vertex is paired with a convex program, and each edge couples two programs through additional convex costs and constraints. We call such a graph a Graph of Convex Sets (GCS). Over a GCS we can formulate any optimization problem that we can formulate over an ordinary weighted graph, with scalar costs on the vertices and edges. In fact, for any fixed choice of the variables in the convex programs, a GCS reduces to a weighted graph where we can seek, e.g., a path, a matching, a tour, or a spanning tree of minimum cost. The challenge in a GCS problem lies in solving the discrete and the continuous components of the problem jointly. By combining the modelling power of graphs and convex optimization, GCSs are a flexible framework to formulate and solve many real-world problems. The graph and the combinatorial goal (e.g., finding a path or a tour) model the high-level discrete skeleton of a problem. The convex costs and constraints fill in the low-level continuous details. The primary contribution of this thesis is an efficient and unified method for solving any GCS problem. Starting from an integer-linear-programming formulation of an optimization problem over a weighted graph, this method formulates the corresponding GCS problem as an efficient Mixed-Integer Convex Program (MICP). This MICP can then be solved to global optimality using common branch-and-bound solvers, or approximately by rounding the solution of its convex relaxation. Importantly, both the formulation of the MICP and its solution are fully automatic, and a user of our framework does not need any expertise in mixed-integer optimization. We first describe the GCS framework and the formulation of our MICP in general terms, without presupposing the specific combinatorial problem to be solved over the GCS. We illustrate our techniques through multiple examples spanning logistics, transportation, scheduling, navigation, and computational geometry. Then we focus on the Shortest-Path Problem (SPP) in GCS. This problem is particularly interesting since it generalizes a wide variety of multi-stage decision-making problems and, using our techniques, it can be solved very effectively. We consider two main applications of the SPP in GCS: optimal control of dynamical systems and collision-free motion iplanning. In these two areas, our techniques either generalize or significantly improve upon algorithms and optimization methods that have been developed for decades and are widely used in academia and industry. Lastly, the techniques introduced in this thesis are implemented in the software packages Drake and gcspy. The former is a large and mature software for robotics. It is open-source and widely used by the community. The second is a very simple and lightweight Python package which is also open source. In this thesis, we will illustrate the usage of gcspy through multiple basic examples.Ph.D
Direct Trajectory Optimization of Robotic Mechanical Systems with Unscheduled Contact Sequences
No full textIn questo studio sono valutate le prestazioni dei metodi di ottimizzazione numerica come mezzi per identificare movimenti dinamici ottimi di sistemi robotici meccanici interagenti con l'ambiente tramite sequenze di contatto non programmate. Nello specifico l'attenzione è concentrata su di uno schematico modello di umanoide bidimensionale (rappresentato come una catena seriale di corpi rigidi a cinque GdL con base fissa nello spazio) impegnato nell'azione di alzarsi (sedersi) da (verso) una posizione supina o prona, entrando in contatto o distaccandosi dal terreno a seconda della necessità tramite l'utilizzo delle mani, dei gomiti, delle anche, delle ginocchia e dei piedi. Le differenti alternative nell'impostazione del problema (che comportano differenti equazioni di vincolo nel processo di ottimizzazione) sono rappresentate dall'introduzione esplicita (o meno) delle forze di contatto tra le variabili libere di ottimizzazione e dalla suddivisione della pianificazione in due successive ottimizzazioni di crescente complessità a livello dinamico. La forma dei comportamenti ottenuti e la sensitività del processo di convergenza sono valutate principalmente al variare dei parametri del modello di contatto e dei pesi associati ai termini della funzione di costo; anche alcune tecniche per guidare l'umanoide ad interagire efficacemente con l'ambiente sono discusse. Lo scopo finale di questo studio è lo sviluppo di una delle poche analisi parametriche complete sulle prestazioni raggiungibili con i metodi di ottimizzazione numerica per la pianificazione del movimento di un intero sistema dinamico con sequenze di contatto non specificate a priori.
This study evaluates the performances of numerical optimization methods as a tool to identify optimal dynamic motions for robotic mechanical systems interacting with the environment through unscheduled contact sequences. Specifically the attention is focuses on a schematic two-dimensional humanoid model (represented as a fixed-base five-DoF articulated serial chain of rigid bodies) in the tasks of getting up (sitting down) from (to) supine and prone positions, opportunistically making and breaking contacts with the ground through hands, elbows, hips, knees, and feet. The different alternatives in the problem transcription (which lead to different constraint equations in the nonlinear program) are determined by the explicit introduction (or not) of contact forces among the free optimization variables and by the split of the planning into two consecutive optimizations of rising dynamic complexity. Shapes of the emergent behaviors and sensitivity of the convergence process are evaluated mainly with respect to contact model parameters and weights of cost function terms; various techniques to guide the humanoid to effectively interact with the environment are also discussed. The final aim of this study is to develop one of the very few complete parametric analysis on the performances achievable with optimization-based methods for whole-body dynamic motion planning with a priori unspecified contact sequences
- …
