In this work, we propose the concept of the Smart Rail, an innovative system for the continuous monitoring of the track geometry based on embedded arrays of Fiber Bragg Grating sensors and Raman-based distributed temperature sensors. First, we discuss how our technology design, based on a custom metallic patch embedding the FBG sensors and brazed on the track, overcomes the robustness concerns of the State of the Art. The metrological principle is formulated based on an analytical/FE model allowing the correlation of the measured signals to the local curvature deformation of the rail, and then to reconstruct the global track geometry. The effect of spatial sampling on the detection of even short-wave defects is addressed through simulations, as being a crucial trade-off between effectiveness and complexity. Experimental results performed on a first prototype demonstrate an efficient strain transfer with excellent agreement with the theoretical predictions. Hence the proposed technology seems very promising for the next generation of monitoring systems, in terms of robustness and compatibility with maintenance operations.

Haptic interaction often requires stabilizing controllers for safety. The Time-Domain Passivity Approach guarantees passivity (then stability) by observing and dissipating energy generated from active elements in a network. The dissipating action is performed by a Passivity Controller, whose action is commanded to the physically limited robot actuators. Thus, the controller stabilizing action should be in turn limited in order to command displayable references to the actuators. This problem is rarely taken into account in the literature and when it is, the limitation is neither directly related to the actuator power limits, nor to the robot's current configuration. The limits of the currently adopted strategies leave room for improvement. In this paper, a new strategy to limit the Passivity Controller action is proposed taking into account both the physical limits of the actuators and the robot configuration. This new strategy is experimentally tested against the classical one based on the sampling time. In the experiment, a human interacts with a virtual wall in a Virtual Environment through a haptic interface. The wall induces an unstable behavior passivated with the two limitation strategies. The results clearly state the benefits introduced by the proposed strategy in two relevant cases.

The accomplishment of a successful teleoperation task requires guaranteeing system stability and transparency. Communication delay (in particular variable time delay), quantization and discretization negatively affect system stability and might be overcome with Time Domain Passivity Approach (TDPA), a model-free and robust way to cope with energy injection due to communication delay. However, this method degrades the transparency of the teleoperation system and worsens tracking performance, introducing in particular position drift error at the slave side and high frequency vibration (jittering) at the master side. In this work, we propose a new joint passivity controller formulation for kinematically redundant manipulators. Our approach stabilizes the system guaranteeing minimal performance loss by privileging the dissipation of the observed energy in the Jacobian null-space. The residual energy (if any) is dissipated in an orthogonal subspace. This is achieved by the solution of an optimization problem with appropriately defined cost functions and constrained to dissipate the energy observed by the passivity observer, guaranteeing the stability of the system. The effectiveness of our algorithm is tested in simulation with both constant and variable time delays.

Search and rescue robotics is becoming a relevant topic in the last years and the growing number of robotic platforms and dedicated projects is the evidence of the interest in this area. In this context, the possibility to drive a remote robot with an exoskeleton is a promising strategy to enhance dexterity, reduce operator effort and save time. However, the use of haptic feedback (bilateral teleoperation) may lead to instability in the presence of communication delay and more complex is the case of bimanual teleoperation where the two arms can exchange energy. In this work, we present a bimanual teleoperation system based on an exoskeletal master, where multi-degrees of freedom (multi-DoFs) and kinematically different devices are involved. In the implemented architecture the two slaves are managed in parallel and independently passivated using the Time Domain Passivity Approach (TDPA) extended for multi-DoFs devices. To investigate the stability of the architecture we designed two tasks highly related to real disaster scenarios: the first one was useful to verify the system behavior in case of small movements and constrained configurations, whereas the second experiment was designed to involve larger contact forces and movements. Moreover, we compared the effect of both delay and low control loop frequency on the stability of the system when TDPA was applied. From the results, it was evident that the overall system exhibited a stable behavior with the use of the TDPA, even passivating the two slaves independently, under simulated time delay and in presence of a low control loop frequency.

In this paper we propose a hybrid fiber optics sensor system, based on Fiber Bragg Gratings (FBG) and Raman distributed temperature sensing (RDTS), for monitoring essential sites within large railway infrastructures like bridges, viaducts and slopes potentially subject to landslides. The geometrical rail track condition is monitored in real-time using fiber optic sensors, providing early warning if pre-defined thresholds are exceeded in terms of longitudinal, horizontal and cross-level defects. The sensor reading units can be remotely located from the monitored zones, without requiring active elements on the tracks and ensuring high immunity to electromagnetic interference. The proposed technology has been first validated in railway laboratories and then in field trials confirming its capability to detect defects over pre-established thresholds and the absence of false alarms with regular train circulation.

This paper presents the development and the experimental validation of a controller for the simulation of the behavior of automotive automatic gearshifts. For this purpose a gearshift simulator was developed based on 2 DOF haptic interface to evaluate users qualitative judgment of automatic gearshifts response. In fact, many car manufacturers use vehicle and primary controls simulators to evaluate the characteristics of a new model before building physical mock-ups or even prototypes. A dedicated control law was designed in order to reproduce different experimentally measured force profiles during forward and backward run of the gearshift handle. The force feedback control law was based on an impedance model with different stiffness values along the path of the gearshift. A state machine selects the characteristics of the force feedback profile according to lever position and velocity. An additional state machine implements the hysteresis behavior of the force profiles by a transition function. The transition algorithm and constraints related to stability are discussed in this paper. The rendered force/position profiles were obtained from experimental data using a real gearshift. Several gearshift response profiles were tested and simulated and experimental results were compared and highlighted good fidelity in force reproduction.

This paper presents a myoelectric control of an arm exoskeleton designed for rehabilitation. A four-muscles-based NeuroMusculoSkeletal (NMS) model was implemented and optimized using genetic algorithms to adapt the model to different subjects. The NMS model is able to predict the shoulder and elbow torques which are used by the control algorithm to ensure a minimal force of interaction. The accuracy of the method is assessed through validation experiments conducted with two healthy subjects performing free movements along the pseudo-sagittal plane. The experiments show promising results for our approach showing its potential for being introduced in a rehabilitation protocol.

A novel wearable haptic device for modulating skin stretch at the fingertip is presented. Rendering of skin stretch in 3 degrees of freedom (DoF), with contact - no contact capabilities, was implemented through rigid parallel kinematics. The novel asymmetrical three revolute-spherical-revolute (3-RSR) configuration allowed compact dimensions with minimum encumbrance of the hand workspace and minimum inter-finger interference. A differential method for solving the non-trivial inverse kinematics is proposed and implemented in real time for controlling the position of the skin tactor. Experiments involving the grasping of a virtual object were conducted using two devices (thumb and index fingers) in a group of 4 subjects: results showed that participants performed the grasping task more precisely and with grasping forces closer to the expected natural behavior when the proposed device provided haptic feedback.

This work presents the development and the preliminary experimental assessment of a novel EMG-driven robotic hand exoskeleton for bilateral active training of grasp motion in stroke. The system allows to control the grasping force required to lift a real object with an impaired hand, through the active guidance provided by a hand active exoskeleton, whose force is modulated by the EMG readings acquired on the opposite unimpaired arm. To estimate the grasping force, the system makes use of surface EMG recordings during grasping, developed on the opposite unimpaired arm, and of a neural network to classify the information. The design, integration and experimental characterization of the system during the grasp of two cylindrical objects is presented. The experimental results show that an optimal force tracking of the interaction force with the object can be achieved.

This paper presents the development of an interaction-torque control architecture for a rehabilitation exoskeleton (RehabExos) with flexible joints equipped with internal torque sensors. The architecture consists of an outer control loop, which is based on the kineto-statics of the RehabExos, and on four identical-independent inner full-state joint-torque controllers (IJTFC). The considered IJTFC demonstrate good stability, responsiveness and accuracy in tracking the desired torques generated by the outer controller. Comparison with other control strategies available from the literature is shown via analytical and experimental results, which highlight the improved performances of the proposed IJTFC method in controlling the RehabExos robot.

Tangential skin displacement at the fingertip is an effective means of communicating direction or displaying static friction in haptic application. A tactile device capable of stretching the skin of the fingerpad can be mounted directly on the fingertip or embedded in haptic interfaces and hand-held devices. In both cases low weight and small dimensions are important requirements. We have developed a miniaturized tactile device capable of displaying tangential skin displacement in two directions. The actuation for the device is realized by SMA wires, in order to reduce bulk and weight, and the displacements are measured by optical sensors. The performance of the device has been verified experimentally.

A linear-quadratic-Gaussian regulator is proposed for the torque control of flexible robotic joints with built-in torque sensor. The regulator requires the joint-torque sensor information only and features: (1) a Kalman filter that, beside reducing the noise and evaluating the derivative of the torque sensor measure, is able to estimate all the external and internal torques acting on the joint; 2) a controller that optimizes system stability, responsiveness, accuracy and effort. The regulator is implemented on a flexible joint of a rehabilitation exoskeleton. Simulation and experimental results are provided which demonstrate regulator performance and efficacy.

In this paper, we present the mechanical design of a new fMRI compatible haptic interface with 3DOFs, based on electrical DC actuation, for the study of brain mechanisms of human motor control. The 1DOF manipulator, which was evaluated successfully on the compatibility with fRMI environment in the preliminary experiments, was extended to the implementation of a 3DOFs parallel manipulator with 3- UPU kinematics. Kinematic properties were studied in different configurations to select the stroke of the prismatic joint and the radius difference between the moving platform and the base. Due to the dimensional constraints imposed by the fMRI environment, the choice of the dimensions and the adopted mechanical solution was a result of an optimization process presented in this work. A further optimization of the mechanical design was then conducted in order to reduce the torque requested to the actuators for gravity compensation and improve the mechanical stiffness with elastic compliance of the manipulator. The final design resulted in a system capable of satisfying all the environment and user requirements.

A new prototype of portable device for haptic interaction with virtual environments is presented. It is a lightweight interface for the fingertips, designed for providing cutaneous feedback and displaying the contact - non contact transition in highly immersive virtual environments. The second version of the interface features a force sensor for controlling the force on the fingertip during contact, assuring a better haptic feedback. In this paper the kinematics, the mechanical design and the improved control system are described. The device has been mounted on a kinesthetic haptic interface which tracks its position: in this configuration, the overall system can provide both cutaneous and kinesthetic feedback and improve the fidelity of the haptic interaction. Finally the performance of the cutaneous device in a task of contour following has been evaluated.

This paper presents a novel method based on screw theory for the analysis of positioning accuracy in parallel manipulators with joint clearances. A general method is introduced, and a new analytical procedure is formulated which allows to determine analytically a sub-optimal estimation of the worst case condition for positioning accuracy. Moreover this procedure can determine exactly the worst-case angular accuracy in translating fully-parallel manipulators under the influence of joint clearances. The relevance of the method is demonstrated by two application examples, that clearly demonstrate how kinematic properties, such as kinematic isotropy, are strictly related to position accuracy in mechanisms with joint clearances.