Massimiliano Solazzi

A fingertip haptic display for improving curvature discrimination

This paper presents a novel haptic device providing both kinesthetic and cutaneous cues informative of shape geometry at the contact point. The system is composed of a supporting kinesthetic haptic interface and an innovative fingertip haptic display that can instantaneously orient a small plate along the tangent plane at the contact point with a virtual shape and bring it in contact with the fingertip. We show how this local augmentation of displayed haptic information can improve human performance in shape exploration, by assessing perception thresholds in curvature discrimination. When kinesthetic feedback was enriched with cutaneous cues, we found a significantly lower threshold for curvature discrimination (1.51 0.2 m-1 vs. 2.62 0.61 m-1, p < .05) for stimuli constituted of spheres with curvature ranging in the interval from 46 m-1. This confirms the importance in haptic perception of the stimulation of cutaneous mechanoreceptors at the fingertip.

An EMG-Controlled Robotic Hand Exoskeleton for Bilateral Rehabilitation

This paper presents a novel electromyography (EMG)-driven hand exoskeleton for bilateral rehabilitation of grasping in stroke. The developed hand exoskeleton was designed with two distinctive features: (a) kinematics with intrinsic adaptability to patients hand size, and (b) free-palm and free-fingertip design, preserving the residual sensory perceptual capability of touch during assistance in grasping of real objects. In the envisaged bilateral training strategy, the patients non paretic hand acted as guidance for the paretic hand in grasping tasks. Grasping force exerted by the non paretic hand was estimated in real-time from EMG signals, and then replicated as robotic assistance for the paretic hand by means of the hand-exoskeleton. Estimation of the grasping force through EMG allowed to perform rehabilitation exercises with any, non sensorized, graspable objects. This paper presents the system design, development, and experimental evaluation. Experiments were performed within a group of six healthy subjects and two chronic stroke patients, executing robotic-assisted grasping tasks. Results related to performance in estimation and modulation of the robotic assistance, and to the outcomes of the pilot rehabilitation sessions with stroke patients, positively support validity of the proposed approach for application in stroke rehabilitation.

Development of a new exoskeleton for upper limb rehabilitation

This paper deals with the development of a novel exoskeleton for the robotic rehabilitation of upper extremities. The system is based on modular custom-designed actuation groups implementing high reduction ratios and redundant position measurement for securing patient safety, and joint torque sensing for guaranteeing system performance and providing application flexibility. Experimental results of the special component prototypes are reported which confirm the validity of the developed actuation groups and the potentials of the proposed exoskeleton architecture.

Wearable Haptic Systems for the Fingertip and the Hand: Taxonomy, Review, and Perspectives

In the last decade, we have witnessed a drastic change in the form factor of audio and vision technologies, from heavy and grounded machines to lightweight devices that naturally fit our bodies. However, only recently, haptic systems have started to be designed with wearability in mind. The wearability of haptic systems enables novel forms of communication, cooperation, and integration between humans and machines. Wearable haptic interfaces are capable of communicating with the human wearers during their interaction with the environment they share, in a natural and yet private way. This paper presents a taxonomy and review of wearable haptic systems for the fingertip and the hand, focusing on those systems directly addressing wearability challenges. The paper also discusses the main technological and design challenges for the development of wearable haptic interfaces, and it reports on the future perspectives of the field. Finally, the paper includes two tables summarizing the characteristics and features of the most representative wearable haptic systems for the fingertip and the hand.

Design of a novel finger haptic interface for contact and orientation display

A new 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. In this paper the kinematics, the mechanical design and the control system are described. The device has been mounted on a kinesthetic haptic interface which tracks its position: the overall system can provide both cutaneous and kinesthetic feedback. Finally the performance of the portable device in a simple task of shape exploration has been evaluated and compared to a kinesthetic haptic interface.

Design of a SMA actuated 2-DoF tactile device for displaying tangential skin displacement

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 wearable fingertip haptic device with 3 DoF asymmetric 3-RSR kinematics

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.

Design of a cutaneous fingertip display for improving haptic exploration of virtual objects

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.

An emg-based robotic hand exoskeleton for bilateral training of grasp

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.

Illusory perception of arm movement induced by visuo-proprioceptive sensory stimulation and controlled by motor imagery

This paper investigates the illusory perception of movement induced through visuo-proprioceptive signals and the possibility of control the illusory movement itself through motor imagery. In particular we evaluated the cross-modal integration of the proprioceptive illusion, induced through vibro-mechanical stimuli, with visual feedback provided by means of a virtual avatar body. The visuo-proprioceptive signals were then integrated as an enhanced feedback for a motor imagery Brain Computer Interface, with the final aim of providing to the user both the perception and mental control of the illusory movement. For this purpose it was specifically developed a system capable of applying vibration stimuli in proximity of the biceps and triceps brachi muscle tendons, and so eliciting the illusory perception of a movement as the vibrated muscle is elongated. We report that the multimodal integration of the proprioceptive illusion with the visual feedback can be successfully induced, though it depends on the subjective perception of speed and onset time of the illusory movement. Moreover we show how it is possible to both perceive and control the avatar body by mental motor imagery through a brain-computer-interface.