A novel hand exoskeleton with series elastic actuation for modulated torque transfer

Abstract Among wearable robotic devices, hand exoskeletons present an important and persistent challenge due to the compact dimensions and kinematic complexity of the human hand. To address these challenges, this paper introduces HandeXos-Beta (HX-β), a novel index finger-thumb exoskeleton for hand rehabilitation. The HX-β system features an innovative kinematic architecture that allows independent actuation of thumb flexion/extension and circumduction (opposition), thus enabling a variety of naturalistic and functional grip configurations. Furthermore, HX-β features a novel series-elastic actuators (SEA) architecture that directly measures externally transferred torque in real-time, and thus enables both position- and torque-controlled modes of operation, allowing implementation of both robot-in-charge and user-in-charge exercise paradigms. Finally, HX-β's adjustable orthosis, passive degrees of freedom, and under-actuated control scheme allow for optimal comfort, robot-user joint alignment, and flexible actuation for users of various hand sizes. In addition to the mechatronic design and resulting functional capabilities of HX-β, this work presents a series of physical performance characterizations, including the position- and torque-control system performance, frequency response, end effector force, and output impedance. By each measure, the HX-β exhibited performance comparable or superior to previously reported hand exoskeletons, including position and torque step response times on the order of 0.3 s, −3 dB cut-off frequencies ranging from approximately 2.5 to 4 Hz, and fingertip output forces on the order of 4 N. During use by a healthy subject in torque-controlled transparent mode, the HX-β orthosis joints exhibited appropriately low output impedance, ranging from 0.42 to −0.042 Nm/rad at 1 Hz, over a range of functional grasps performed at real-life speeds. This combination of lab bench characterizations and functional evaluation provides a comprehensive verification of the design and performance of the HandeXos Beta exoskeleton, and its suitability for clinical application in hand rehabilitation

Identification of Linear Time Periodic Systems via Harmonic Transfer Function. Theory and Application on a Helicopter Rotor Model

L'analisi di Sistemi Lineari Tempo-Periodici (LTP) trova applicazioni in problemi ingegneristici dove le dinamiche sono rappresentabili attraverso un set di equazioni differenziali a coefficienti periodici, linearizzate attorno a una condizione nominale. I sistemi LTP sono rappresentabili in uno spazio di stato con matrici (degli stati, degli ingressi, delle uscite e di accoppiamento ingressi-uscite) periodiche. Le Lifting Techniques permettono di rappresentare i sistemi LTP attraverso relazioni ingresso-uscita analoghe a quelle di sistemi Linear Tempo-Invarianti: il Frequency Lifting in particolare fornisce una rappresentazione accresciuta LTI Multi-Input-Multi-Output (MIMO), da ogni modulazione (con multipli della frequenza tipica del sistema) dell'ingresso verso ogni modulazione (con multipli della frequenza tipica del sistema) dell'uscita. La matrice delle funzioni di trasferimento corrispondente è nota come Harmonic Transfer Function (HTF). In questa tesi è presentata la derivazione teorica e l'implementazione di un algoritmo di identificazione volto a ricavare un'approssimazione troncata qualsiasi della HTF, utilizzando una serie di ingressi propriamente scelti e le uscite derivantine. Ne è presentata infine un' applicazione su un modello numerico di un rotore di elicottero

Phase-II Clinical Validation of a Powered Exoskeleton for the Treatment of Elbow Spasticity

Introduction: Spasticity is a typical motor disorder in patients affected by stroke. Typically post-stroke rehabilitation consists of repetition of mobilization exercises on impaired limbs, aimed to reduce muscle hypertonia and mitigate spastic reflexes. It is currently strongly debated if the treatment's effectiveness improves with the timeliness of its adoption; in particular, starting intensive rehabilitation as close as possible to the stroke event may counteract the growth and postpone the onset of spasticity. In this paper we present a phase-II clinical validation of a robotic exoskeleton in treating subacute post-stroke patients.Methods: Seventeen post-stroke patients participated in 10 daily rehabilitation sessions using the NEUROExos Elbow Module exoskeleton, each one lasting 45 min: the exercises consisted of isokinetic passive mobilization of the elbow, with torque threshold to detect excessive user's resistance to the movement. We investigated the safety by reporting possible adverse events, such as mechanical, electrical or software failures of the device or injuries or pain experienced by the patient. As regards the efficacy, the Modified Ashworth Scale, was identified as primary outcome measure and the NEEM metrics describing elbow joint resistance to passive extension (i.e., maximum extension torque and zero-torque angle) as secondary outcomes.Results: During the entire duration of the treatments no failures or adverse events for the patients were reported. No statistically significant differences were found in the Modified Ashworth Scale scores, between pre-treatment and post-treatment and between post-treatment and follow-up sessions, indicating the absence of spasticity increase throughout (14 days) and after (3–4 months follow-up) the treatment. Exoskeleton metrics confirmed the absence of significant difference in between pre- and post-treatment data, whereas intra-session data highlighted significant differences in the secondary outcomes, toward a decrease of the subject's joint resistance.Conclusions: The results show that our robotic exoskeleton can be safely used for prolonged sessions in post-stroke and suggest that intensive early rehabilitation treatment may prevent the occurrence of spasticity at a later stage. Moreover, the NEEM metrics were found to be reliable compared to the Modified Ashworth Scale and sensitive to revealing intra-session changes of elbow resistance to passive extension, in agreement with clinical evidences

A clutch mechanism for switching between position and stiffness control of a variable stiffness actuator

Variable stiffness actuators (VSA) are fostered in robotics for their capability to address physical interaction with a physically adjustable compliance, being advantageous in terms of efficiency, safety and adaptability to unknown environments. Here we introduce the concept of a switching VSA (sVSA), in which a single actuator is used to control the position or the stiffness of a robotic joint according to a mechanical switch. Despite not allowing simultaneous control of both quantities, this architecture has the potential to make the design lighter, requiring one continuously powered actuator, controllable in position, and one additional switch, activated only occasionally between two limit stages: the advantages are the separation of the motors power requirements and a simpler control. A first prototype of a 1-DoF revolute variable-stiffness joint has been built, based on the vsaUT-II developed at the University of Twente, with a novel clutch mechanism allowing continuous and efficient switching. The prototype proved functionality and feasibility of the sVSA concept

Review of Assistive Strategies in Powered Lower-Limb Orthoses and Exoskeletons

Starting from the early research in the 1960s, especially in the last two decades, orthoses and exoskeletons have been significantly developed. They are designed in different architectures to assist their users’ movements. The research literature has been more prolific on lower-limb devices: a main reason is that they address a basic but fundamental motion task, walking. Leg exoskeletons are simpler to design, compared to upper-limb counterparts, but still have particular cognitive and physical requirements from the emerging human–robot interaction systems. In the state of the art, different control strategies and approaches can be easily found: it is still a challenge to develop an assistive strategy which makes the exoskeleton supply efficient and natural assistance. So, this paper aims to provide a systematic overview of the assistive strategies utilized by active locomotion–augmentation orthoses and exoskeletons. Based on the literature collected from Web of Science and Scopus, we have studied the main robotic devices with a focus on the way they are controlled to deliver assistance; the relevant validations are as well investigated, in particular experimentations with human in the loop. Finally current trends and major challenges in the development of an assistive strategy are concluded and discussed