In this paper we pursue an investigation on the role of perceptual flow in the tactile domain, which appears to be a primary source for information such as shape, motion and softness. In this paper, we report on a set of psychophysical experiments involving how humans integrate incoherent tactile flow stimuli. Two experiments are reported, whereby discordant stimuli are conveyed to the subject by two different fingertips, or by two different families of mechanoreceptors in the same finger. Results from the first experiment show that, in these conditions, the tactile and the optic perceptive systems act in a very similar way. In the second experiment the interaction between tactile flow and friction generate an illusory phenomenon peculiar of the tactile system.
V5/MT complex responds selectively to perception of optic flow (Morrone et al., Nature Neurosci , 2001). Since similarities exist between visual and tactile perception, we hypothesized that tactile flow might also rely on V5/MT response. We and others have shown recently that visual extrastriate cortical areas respond both during visual and tactile recognition of objects, indicating that these regions are organized in a supramodal fashion. In this study, we measured neural response evoked during visual and tactile perception of coherently moving dot patterns to test the hypothesis that V5/MT may be supramodally organized and may respond also to tactile stimulation.
In this paper we describe a design of an innovative immersive Haptic Black Box (HBB) based on Magneto Rheological Fluids (MRF). By exploiting results from an accurate analysis performed on a previously operating haptic display a new device capable of exciting the MRF with improved performance in terms of magnetic field intensity and spatial resolution has been developed. Due to the core structure and feeding conditions, only a 3D numerical analysis, taking into account the material non-linearity, provides an accurate prediction of the excitation field and, consequently, of the rheological behavior of the uid. The results of the present paper will be used in subsequent work where the realization of the prototype and the results of several psychophysical tests on excited MRF in terms of softness and/or shape reconstruction will be described.
In a previous paper, a device for the characterization of MagnetoRheological Fluids (MRF) has been described. The MRF consist of micro-sized, magnetically active particles dispersed in a carrier medium. When exposed to a magnetic field, MRF change their own consistency turning from fluid to near-solid state responding to the applied field within milliseconds. This interesting property, suggests the possibility to use magnetorheological fluids to mimic the compliance of biological tissues in order to realize a haptic display, such as in surgical training for minimally invasive surgery and/or open surgery simulations [2]. In this scenario the operator could interact with a virtual object which simulate several biological tissues by magnetically tuning the rheological properties of the fluid. In this paper an accurate analysis of an immersive device for the magnetic excitation of the fluid is presented. In particular such analysis is focused on a system of ferromagnetic "pistons", that, properly positioned in the device, can address the magnetic flux in the MRF.
We report results of a pilot study using functional magnetic resonance imaging aimed at determining the neural correlates of tactile flow. We hypothesized that brain response to tactile flow would involve the same cortical areas (V5/MT) that respond to optic flow. Our results showed that V5/MT cortex indeed is activated by tactile flow perception. These findings are consistent with a supramodal organization of brain regions involved in optic and tactile flow processing.
In this paper we consider the problem of controlling multiple scalar systems through a limited capacity shared channel. Each system is affected by process noise and can be controlled byactuators with values in a {\em fixed}inite set. The control objective is to bound the evolution of the systems in specified sets (controlled invariance). Our goal is to find an optimal allocation of the shared communication resource to the different control activities and to identify correct choices for the design parameters. The paper provides fundamental conceptual tools to attack the design problem in the formal framework of an optimization problem. Namely, we give a feasibility criterion to decide whether a set of design parameters conforms with a control specification (i.e., with the controlled invariance of a specified set for each system). Moreover, we offer the explicit computation of the minimum bit rate necessary for the controlled invariance of a set, which is of utmost importance for solving the optimization problem.
Linear dynamical systems controlled by quantized inputs exhibit phenomena which are typically non-linear, including chaotic behaviours. We consider discrete-time single-input models of the type x(k+1)=Ax(k)+bu(k). The construction of invariant sets for this class of hybrid systems is of utmost importance for the stabilization problem. We first review a technique to construct invariant sets when an arbitrary quantized input set is assigned. We hence study minimality properties for invariant sets when inputs take integer values. There is a relation between a so-called strong minimality property and ergodicity of the closed-loop dynamics, in particular, ergodicity implies strong minimality. A condition ensuring strong minimality is given in terms of the coefficients of the characteristic polynomial of the matrix 'A'. Two examples are presented: the first one shows that strong minimality does not imply ergodicity. The second one shows that our condition for strong minimality is only sufficient: this is done by exhibition of an ergodic dynamics for which our condition is not satisfied.
In this paper we propose a new approach to motion planning, based on the introduction of a lattice structure in the workspace of the robot, leading to efficient computations of plans for rather complex vehicles, and allowing for the implementation of optimization procedures in a rather straightforward way. The basic idea is the purposeful restriction of the set of possible inputfunctions to the vehicle to a finite set of symbols, or {\em control quanta},which, under suitable conditions, generate a regular lattice of reachable points. Once the lattice is generated and a convenient description computed, standard techniques in integer linear programming can be used to find a plan very efficiently. We also provide a correct and complete algorithm to the problem of finding an optimized plan (with respect e.g. to length minimization) consisting in a sequence of graph searches.
In this paper we consider policies for cooperative, decentralized traffic management among a number of autonomous mobile agents. The conflict resolution problem is addressed considering realistic restrictions on possible maneuvers. We formulate this problem as one in Mixed Integer Linear Programming (MILP). The method, which proves successful in a centralized implementation with a large number of cooperating agents, is also extended to a decentralized setting. Conditions for the existence of conflict avoidance maneuvers for a system of 5 autonomous agents with a transitive information structure are provided, along with the explicit policy to be applied by each agent.
The purpose of this document is to provide a compatibility test for mechatronic devices to be used within a diagnostic MR environment. In order to design new devices that can produce tactile stimuli of different nature inside the MRI environment, compatibility tests with several materials and mechatronic devices are reported. Results of these experiments are analyzed in order to evaluate artefacts caused by the presence and actuation of the devices.
In this paper we consider the problem of navigating an autonomous robot using primarily vision for localizing the robot, building a map of the environment, and navigating through viapoints to goals. A visual servo scheme is used that can steer the wheeled vehicle among images. Goal images do not necessarily correspond to images physically taken from the desired vehicle posture, as servoing to reconstructed virtual images is possible. A topological image map is constructed to support this, based on images grabbed by on-board cameras, along with a global feature-based metric map, using extended Kalman filter techniques. The method also enables a team of multiple vehicles to merge their information, and to coordinate navigation using each other's images. Realistic assumptions on limited communication bandwidth between agents and available memory storage are taken into account considering informative, memory-safe maps. Simulations and preliminary experimental results on a laboratory setup are reported.
Development of a Wearable System Based on Smart Textiles and GPRS Transmission for Remote Multiparametric Monitoring of Cardiac Patients: Preliminary Results of the WEALTHY Project
This paper describes a new generation of actuators for robotic applications, and more generally for machines that are designed to interact with humans. Such actuators, called Variable Impedance Actuators, are designed to achieve fast motion control while guaranteeing safety of human operators in worst-case impact situation. The fundamental innovation is to implement safety by purely mechanical, passive means, to guarantee intrinsic safety, while active control is used to recover performance. The design concept, which is the subject of a patent application, has led to the experimental implementation of a Variable Stiffness Actuator. The effectiveness of the VSA has been recently validated theoretically and experimentally by authors.
In this paper the synthesis and design of a new device for the energization and characterization of Magneto-Rheological Fluids (MRF) for haptic interfaces are presented. Due to the core structure and feeding conditions, only a 3D numerical analysis provides an accurate prediction of the electromagnetic quantities and the rheological behavior of an excited specimen. The design constraints are shown in details and the results in terms of magnetic field inside the fluid and its spatial resolution are discussed.
In this paper we consider the generalization of the classical notion of nonholonomy of smooth constraints in analytical mechanics, to a substantially wider set of systems, allowing for discrete and hybrid (mixed continuous and discrete) configurations and transitions. We show that the general notion of nonholonomy can be captured by the definition of two different types of nonholonomicbehaviours, which we call {\em internal}nd {\em external}, respectively. Examples are reported of systems exhibiting either the former only, or the latter only, or both. For some classes of systems, we provide equivalent or sufficient characterizations of such definitions, which allow for practical tests.
Traditional control design is based on ideal assumptions concerning the amount, type and accuracy of the information flow that can be circulated across the controller. Unfortunately, real implementation platforms exhibit non-idealities that may substantially invalidate such assumptions. As a result, the systems closed-loop performance can be severely affected and sometimes stability itself is jeopardised. These problems show up with particular strength when multiple feedback loops share a limited pool of computation and communication resources. In this case the designer is confronted with the challenging task of choosing at the same time the control law and the optimal allocation policy for the shared resources (control algortihm/system architecture co-design).
The work describes on-going work at the University of Pisa on the field of tele-laboratories and distance learning. In particular, the group is working at the evolution of existing tele-laboratory experiments in the field of robotics and control into learning units of a self-consistent didactic project. The pick-and-place system described has been designed to provide the set-up for robot arm motion planning with specific objectives and evaluation tools.
Rolling a ball on a plane is a standard example of nonholonomy reported in many textbooks, and the problem is also well understood for any smooth deformation of the surfaces. For non-smoothly deformed surfaces, however, much less is known. Although it may seem intuitive that nonholonomy is conserved (think e.g. to polyhedral approximations of smooth surfaces), current definitions of ``nonholonomy'' are inherently referred to systems described by ordinary differential equations, and are thus inapplicable to such systems. \İn this paper we study the set of positions and orientations that a polyhedral part can reach by rolling on a plane through sequences of adjacent faces. We provide a description of such reachable set, discuss conditions under which the set is dense, or discrete, or has a compound structure, and provide a method for steering the system to a desired reachable configuration, robustly with respect to model uncertainties. \\Based on ideas and concepts encountered in this case study, and in some other examples we provide, we turn back to the most general aspects of the problem and investigate the possible generalization of the notion of (kinematic) nonholonomy to non-smooth, discrete, and hybrid dynamical systems. To capture the essence of phenomena commonly regarded as ``nonholonomic'', at least two irreducible concepts are to be defined, of ``internal'' and ``external'' nonholonomy, which may coexist in the same system. These definitions are instantiated by examples.
In this chapter, we consider three of the main problems that arise in the navigation of autonomous vehicles in partially or totally unknown environments, i.e. building a map of the environment, self-localizing, and servoing the robot so as to achieve given goals based on sensorial information. As compared to most part of the existing literature on SLAM, we privilege here a system-theoretic view to the problem, which allows the localization and mapping problems to be cast in a unified framework with the control problem. The chapter is an overview of existing results in this vein, and of some interesting directions for research in the field. All chapters of this volume were revised and published online March 2005. The volume number was corrected from 4010 to 10.
In this paper we consider the mobile robot parking problem, i.e. the stabilization of a wheeled vehicle to a given position and orientation, using only visual feedback from low-cost cameras. The practically most relevant problem of keeping the tracked features in sight of the camera while maneuvering to park the vehicle is taken into account. This constraint, often neglected in the literature, combines with the nonholonomic nature of the vehicle kinematics in a challenging controller design problem. We provide an effective solution to such problem by using a combination of previous results on non-smooth control synthesis and recently developed hybrid control techniques. Simulations and experimental results on a laboratory vehicle are reported, showing the practicality of the proposed approach.
In this paper we discuss the problem of achieving good performance in accuracy and promptness by a robot manipulator under the condition that safety is guaranteed throughout task execution. The particular but basic problem of single-joint actuation is considered in detail. Intuitively, while a rigid and powerful structure of the arm would favour its performance, lightweight compliant structures are more suitable to safe operation. The quantitative analysis of the resulting design trade-off between safety and performance is one of the objectives of our work. Such analysis has a strong impact on how robot mechanisms and controllers should be designed for human-interactive applications. We discuss few different possible concepts for safely actuating joints, and focus our attention on one, the Variable-Stiffness Transmission (VST) approach. Some aspects related to the implementation of the mechanics and control of VST joints are reported.
Notes
PUBLISHER'S NOTE: In this paper, there are three errors introduced during production. First, the correct title of the article is Fast and Soft Arm Tactics. Also, on formulae for GSI and HIC in page 23, the acceleration is measured in multiples of the acceleration of gravity (g) [not grams], while time is measured in seconds. Finally, within Figure 1, one should read Compliant Covering, and Mrob = Mrotor + Mlink [instead of Krob = Krotor + Klink]. Please visit http://www.ncsu.edu/IEEE-RAS/RAM/BicchiFigure1.pdf to see the original figure.
