In this paper, we consider a decentralized cooperative control policy proposed recently for steering multiple non-holonomic vehicles between assigned start and goal configurations while avoiding collisions. The policy is known to ensure safety (i.e., collision avoidance) for an arbitrarily large number of vehicles, if initial configurations satisfy certain conditions. The method is highly scalable, and effective solutions can be obtained for several tens of autonomous agents. On the other hand, the liveness property of the policy, i.e. the capability of negotiating a solution in finite time, is not yet completely understood. In this paper, we introduce a condition on the final vehicle configurations, which we conjecture to be sufficient for guaranteeing liveness. Because of the overwhelming complexity of proving the sufficiency of such condition, we assess the correctness of the conjecture in probability through the analysis of the results of a large number of randomized experiments.
This work is concerned with the practical stabilization of discrete–time SISO linear systems under assigned quantization of the input and output spaces. A controller is designed which guarantees effective practical stability properties. Unlike most of the existing literature, quantization is supposed to be a problem datum rather than a degree of freedom in design. Moreover, in the framework of control under assigned quantization, results are concerned with state quantization only and do not include the quantized output feedback case considered here. While standard stability analysis techniques are based on Lyapunov theory and invariant ellipsoids, our study of the closed loop dynamics involves a particularly suitable family of sets, which are hypercubes in controller form coordinates.
This paper is concerned with exploring the possibility of using Magneto-Rheological Fluids (MRF) as haptic interface. MRF are special materials capable of changing their rheological behaviour with an external magnetic field. This property suggested us to use MRF to mimic virtual objects whose compliance can be gradually modulated. Several architectures of prototypes have been envisaged. The general scheme of both prototypes refers to a Haptic Black Box (HBB) concept, intended as a box where the operator can poke his/her bare hand, and interact with the virtual object by freely moving the hand without mechanical constraints. In this way sensory receptors on the whole operator
In this paper we report on a new improved free-hand haptic interface based on magnetorheological fluids (MRFs). MRFs are smart materials which change their rheology according to an external magnetic field. The new architecture here proposed results from the development and improvement of earlier prototypes. The innovative idea behind this device is to allow subjects interacting directly with an object, whose rheology is rapidly and easily changeable, freely moving their hands without rigid mechanical linkages. Numerical advanced simulation tests using algorithms based on finite element methods have been implemented, in order to analyze and predict the spatial distribution of the magnetic field. A special focus was laid on investigating on how the magnetic filed profile is altered by the introduction of the hand. Possible solutions were proposed to overcome this perturbation. Finally some preliminary psychophysical tests in order to assess the performance of the device are reported and discussed.
A previous result about uniform global asymptotic stability (UGAS) of the equilibrium of a cascaded time-varying systems, is here also shown to hold for closed (not necessarily compact) sets composed by set-stable subsystems of a cascade. In view of this result an optimal control allocation approach is discussed.
The design of automotive control systems is becoming increasingly complex as the level of performance required by car manufactures grows continuously and the constraints on cost and development time imposed by the market become tighter. A successful design, without costly and time consuming re-design cycles, can be achieved only by using an efficient design methodology that allows for component re-use and evaluation of platform requirements at the early stages of the design flow. In this paper, we illustrate a control-implementation design methodology for the development of embedded controllers by composition of algorithms picked up from libraries. Randomized algorithms and hybrid system theory are used to develop techniques for functional and architecture evaluations, which are implemented in a prototype tool.
In this paper we describe the motivations and the aim ofthe EURON-2 research project ``\underline{P}hysical \underline{H}uman-\underline{R}obot \underline{I}nteraction in Anthropic \underline{Dom}ains'' (PRHIDOM). This project, which moves along the lines indicated by the 1$^{st}$ IARP/IEEE-RAS Workshop on Technical Challenge for Dependable Robots in Human Environments \cite{iarp01}, is about ``charting'' the new ``territory'' of physical Human-Robot Interaction (pHRI). To ensure these goals, the integration competences in control, robotics, design and realization of mechanical systems, human-machine interaction, and in safety-dependability of mechatronic systems is required. The PHRIDOM Consortium is composed of 5 partners from 3 different European countries.
The design and development of computational infrastructures supporting existing tele-laboratory experiences in the field of automation and robotics are described. The goal of the activity is to provide a proper e-learning environment in which remote laboratory experiences are integrated in a coherent way. The addition of e-learning features, as self-assessment and progress monitoring tools, asynchronous tutor interaction, authentication, evaluation and follow-up features, has led also to the modification of the original tele-laboratory set-up.
In this paper we report on results of a psychophysical experiment in which the optic illusion of Ouchi is reproduced in the tactile domain. In the vision field, when eyes scan over a texture grid, consisting in two rectangular checkerboard patterns oriented in orthogonal directions, the inset pattern appears to move relatively to the surrounding grid. A simplified 3D version of this pattern was realized and a group of subjects were asked to touch it while it was vibrating. Outcomes of this experiment are discussed in terms of tactile flow and the related aperture problem.
In this paper we report on results of a set of tests in which a group of subjects were asked to trace a straight line with the forefinger while actively scanning over a textured surface. A pattern of bumped dots, randomly distributed, and a diagonal striped pattern were used in order to investigate the occurrence of misleading perceptions based on the aperture problem of tactile flow during an active exploration. Obtained results are compared with findings achieved from a previous experiment based on passive exploration.
In this paper, we present a method to control casting manipulation by means of real-time visual feedback. Casting manipulation is a technique to deploy a robotic end-effector at large distances from the robot's base, by throwing the end-effector and controlling its ballistic flight using forces transmitted through a light tether connected to the end-effector itself. The tether cable can also be used to retrieve the end-effector and exert forces on the robot's environment. Previous work has shown that casting manipulation is able to catch objects at a large distance, proving it viable for applications such as sample acquisition and return, rescue, etc. In previous experiments, the position of the target object was known exactly. In this paper, we present a first attempt at closing a real-time control loop on casting manipulation using visual feedback of moving targets. As accurate planning methods developed for off-line open-loop planning cannot be used in real-time, we develop a simplified model and control algorithm, whose effectiveness is demonstrated through experiments.
Notes
(ICRA05 B. Wegbreit Award for Best Manipulation Paper)
We address the following fundamental question: given a double integrator and a linear control that stabilizes it exponentially, is it possible to use the {\em same} control input in the case that the control input is multiplied by a time-varying term? Such question has many interesting motivations and generalizations: 1) we can pose the same problem for an input gain that depends on the state and time hence, a specific persistency of excitation property for nonlinear systems must be imposed; 2) the stabilization –with the same method– of chains of integrators of higher order than two is fundamentally more complex and has applications in the stabilization of driftless systems; 3) the popular backstepping method stabilization method for systems with non-invertible input terms. The purpose of this note is two-fold: we present some open questions that we believe are significant in time-varying stabilization and present some preliminary answers for simple, yet challenging case-studies.
In this paper, we consider the problem of collision-free motion planning for multiple nonholonomic planar vehicles. Each vehicle is capable of moving at constant speed along paths with bounded curvature, and is aware of the position and heading of other vehicles within a certain sensing radius. No other information exchange is required between vehicles. We propose a spatially decentralized, cooperative hybrid control policy that ensures safety for arbitrary numbers of vehicles. Furthermore, we show that under certain conditions, the policy avoids dead- and livelock, and eventually all vehicles reach their intended targets. Simulations and experimental results are presented and discussed.
Supramodal response of human MT+ complex to visual and tactile perception of flow as demonstrated by fMRI studies in sighted and congenitally blind individuals
Publication Type
Conference Paper
Year of Publication
2005
Conference Name
11th annual meeting of the organization for Human Brain Mapping
