Wearability will significantly increase the use of haptics in everyday life, as has already happened for audio and video technologies. The literature on wearable haptics is mainly focused on vibrotactile stimulation, and only recently, wearable devices conveying richer stimuli, like force vectors, have been proposed. This paper introduces design guidelines for wearable haptics and presents a novel 3-DoF wearable haptic interface able to apply force vectors directly to the fingertip. It consists of two platforms: a static one, placed on the back of the finger, and a mobile one, responsible for applying forces at the finger pad. The structure of the device resembles that of parallel robots, where the fingertip is placed in between the static and the moving platforms. This work presents the design of the wearable display, along with the quasi-static modeling of the relationship between the applied forces and the platform's orientation and displacement. The device can exert up to 1.5 N, with a maximum platform inclination of 30 degree. To validate the device and verify its effectiveness, a curvature discrimination experiment was carried out: employing the wearable device together with a popular haptic interface improved the performance with respect of employing the haptic interface alone.

One of the major limitations to the use of advanced robotic hands in industries is the complexity of the control system design due to the large number of motors needed to actuate their degrees of freedom. It is our belief that the development of a unified control framework for robotic hands will allow us to extend the use of these devices in many areas. Borrowing the terminology from software engineering, there is a need for middleware solutions to control the robotic hands independently from their specific kinematics and focus only on the manipulation tasks. To simplify and generalize the control of robotic hands, we take inspiration from studies in neuroscience concerning the sensorimotor organization of the human hand. These studies demonstrated that, notwithstanding the complexity of the hand, a few variables are able to account for most of the variance in the patterns of configurations and movements. The reduced set of parameters that humans effectively use to control their hands, which are known in the literature as synergies, can represent the set of words for the unified control language of robotic hands, provided that we solve the problem of mapping human hand synergies to actions of the robotic hands. In this study, we propose a mapping designed in the manipulated object domain in order to ensure a high level of generality with respect to the many dissimilar kinematics of robotic hands. The role of the object is played by a virtual sphere, whose radius and center position change dynamically, and the role of the human hand is played by a hand model referred to as ``paradigmatic hand,'' which is able to capture the idea of synergies in human hands

a b s t r a c tThe prediction of the wear at the wheel-rail interface is a fundamental problem in the railway field, mainly correlated to the planning of maintenance interventions, vehicle stability and the possibility of researching specific strategies for the wheel and rail profile optimization. In this work the Authors present a model specifically developed for the evaluation of the wheel and rail profile evolution due to wear, whose layout is made up of two mutually interactive but separate units: a vehicle model for the dynamic analysis and a model for the wear estimation. The first one is made up of two parts that interact online during the dynamic simulations: a 3D multibody model of the railway vehicle implemented in Simpack Rail (a commercial software for the analysis of multibody systems) and an innovative 3D global contact model (developed by the Authors in previous works) for the detection of the contact points between wheel and rail and for the calculation of the forces in the contact patches (implemented in C/C++environment). The wear model, implemented in the Matlab environment, is mainly based on experimental relationships found in literature between the removed material and the energy dissipated by friction at the contact. It starts from the outputs of the dynamic simulations (position of contact points, contact forces and global creepages) and calculates the pressures inside the contact patches through a local contact model (FASTSIM algorithm); then the material removed due to wear is evaluated and the worn profiles of wheel and rail are obtained. This approach allows the evaluation of both the quantity of removed material and its distribution along the wheel and rail profiles in order to analyze the development of the profiles shape during their lifetime.The whole model is based on a discrete process: each discrete step consists in one dynamic simulation and one profile update by means of the wear model while, within the discrete step, the profiles are supposed to be constant. The choice of an appropriate step is fundamental in terms of precision and computational load. Moreover the different time scales characterizing the wheel and rail wear evolution require the development of a suitable strategy for the profile update: the strategy proposed by the Authors is based both on the total distance traveled by the considered vehicle and on the total tonnage burden on the track. The entire model has been developed and validated in collaboration with Trenitalia S.p.A. and Rete Ferroviaria Italiana (RFI), which have provided the technical documentation and the experimental results relating to some tests performed with the vehicle DMU Aln 501 Minuetto on the Aosta-Pre Saint Didier line.

Cutaneous haptic feedback can be used to enhance the performance of robotic teleoperation systems while guaranteeing their safety. Delivering ungrounded cutaneous cues to the human operator conveys in fact information about the forces exerted at the slave side and does not affect the stability of the control loop. In this work we analyze the feasibility, effectiveness, and implications of providing solely cutaneous feedback in robotic teleoperation. We carried out two peg-in-hole experiments, both in a virtual environment and in a real (teleoperated) environment. Two novel 3-degree-of-freedom fingertip cutaneous displays deliver a suitable amount of cutaneous feedback at the thumb and index fingers. Results assessed the feasibility and effectiveness of the proposed approach. Cutaneous feedback was outperformed by full haptic feedback provided by grounded haptic interfaces, but it outperformed conditions providing no force feedback at all. Moreover, cutaneous feedback always kept the system stable, even in the presence of destabilizing factors such as communication delays and hard contacts.

To adapt to many different objects and tasks, hands are very complex systems with many degrees of freedom (DoFs), sensors, and actuators. In robotics, such complexity comes at the cost of size and weight of the hardware of devices, but it strongly affects also the ease of their programming. A possible approach to simplification consists in coupling some of the DOFs, thus affording a reduction of the number of effective inputs, and eventually leading to more efficient, simpler, and reliable designs. Such coupling can be at the software level, to achieve faster, more intuitive programmability or at the hardware level, through either rigid or compliant physical couplings between joints. Physical coupling between actuators and simplification of control through the reduction of independent inputs is also an often-reported interpretation of human hand movement data, where studies have demonstrated that few "postural synergies" explain most of the variance in hand configurations used to grasp different objects. Together with beneficial simplifications, the reduction of the number of independent inputs to a few coupled motions or "synergies" has also an impact on the ability of the hand to dexterously control grasp forces and in-hand manipulation. This paper aims to develop tools that establish how many synergies should be involved in a grasp to guarantee stability and efficiency, depending on the task and on the hand embodiment. Through the analysis of a quasi-static model, grasp structural properties related to contact force and object motion controllability are defined. Different compliant sources are considered, for a generalization of the discussion. In particular, a compliant model for synergies assumed, referred to as "soft synergies," is discussed. The controllable internal forces and motions of the grasped object are related to the actuated inputs. This paper investigates to what extent a hand with many joints can exploit postural synergies to control force and motion of the grasped object

The complexity of robotic hands is needed to adapt devices to the many kinds of tasks, but the large number of motors needed to fully actuate the DoFs comes at the cost of size, complexity and weight of devices. A possible approach to solve this problem consists of reducing the number of actuators thus resulting more efficient, simpler and reliable than their fully actuated alternatives. Reducing control inputs seems to inspire also biological systems and in particular motor control of human hands, which share with robotic hands the large number of DoFs. Recent studies demonstrated that a few control variables, named postural synergies, are able to account for most of the variance in the patterns of hand movements and configurations of hands. This paper focuses on hands with postural synergies. Reducing the number of control inputs, from fully actuated joints to few synergies, might reduce the dimension of the force and motion controllability subspaces thus compromising the dexterity of the grasp, however, this is not true in general but strongly depends on how synergies are distributed. The paper investigates to what extent a hand with many DoFs can exploit postural synergies to control force and motion of the grasped object.

The multibody simulation of railway vehicle dynamics needs a reliable and efficient method to evaluate the contact points between wheel and rail, because their positions have a considerable influence on the direction and intensity of the contact forces. In this work, an innovative semi-analytic procedure for the detection of the wheel/rail contact points (named the DIFF method) is presented. This method considers the wheel and the rail as two surfaces whose analytic expressions are known and is based on the idea that in the contact points the difference between the surfaces has local minima and is equivalent to solving an algebraic two-dimensional system. The original problem can be reduced analytically to a simple scalar equation that can be easily solved numerically (since the problem dimension is one, even elementary non-iterative algorithms can be efficient).

Wearable technologies are gaining great popularity in the recent years. The demand for devices that are lightweight and compact challenges researchers to pursue innovative solutions to make existing technologies more portable and wearable. In this paper we present a novel wearable cutaneous fingertip device with 3 degrees of freedom. It is composed of two parallel platforms: the upper body is fixed on the back of the finger, housing three small servo motors, and the mobile end-effector is in contact with the volar surface of the fingertip. The two platforms are connected by three articulated legs, actuated by the motors in order to move the mobile platform toward the user's fingertip and re-angle it to simulate contacts with arbitrarily oriented surfaces. Each leg is composed of two rigid links, connected to each other and then to the platforms, according to a RRS (Revolute-Revolute-Spherical) kinematic chain. With respect to other similar cable-driven devices presented in the literature, this device solves the indeterminacy due to the underactuation of the platform. This work presents the main design steps for the development of the wearable display, along with its kinematics, quasi-static modeling, and control. In particular, we analyzed the relationship between device performance and its main geometrical parameters. A perceptual experiment shows that the cutaneous device is able to effectively render different platform configurations