Sasha B. Godfrey

Robotic Approaches for Rehabilitation of Hand Function After Stroke

ABSTRACTThe goal of this review was to discuss the impairments in hand function after stroke and present previous work on robot-assisted approaches to movement neurorehabilitation. Robotic devices offer a unique training environment that may enhance outcomes beyond what is possible with conventional means. Robots apply forces to the hand, allowing completion of movements while preventing inappropriate movement patterns. Evidence from the literature is emerging that certain characteristics of the human-robot interaction are preferable. In light of this evidence, the robotic hand devices that have undergone clinical testing are reviewed, highlighting the authors’ work in this area. Finally, suggestions for future work are offered. The ability to deliver therapy doses far higher than what has been previously tested is a potentially key advantage of robotic devices that needs further exploration. In particular, more efforts are needed to develop highly motivating home-based devices, which can increase access to high doses of assisted movement therapy.

Proceedings of the first workshop on peripheral machine interfaces: Going beyond traditional surface electromyography

One of the hottest topics in rehabilitation robotics is that of proper control of prosthetic devices. Despite decades of research, the state of the art is dramatically behind the expectations. To shed light on this issue, in June, 2013 the first international workshop on Present and future of non-invasive peripheral nervous system (PNS)–Machine Interfaces (MI; PMI) was convened, hosted by the International Conference on Rehabilitation Robotics. The keyword PMI has been selected to denote human–machine interfaces targeted at the limb-deficient, mainly upper-limb amputees, dealing with signals gathered from the PNS in a non-invasive way, that is, from the surface of the residuum. The workshop was intended to provide an overview of the state of the art and future perspectives of such interfaces; this paper represents is a collection of opinions expressed by each and every researcher/group involved in it.

Exploring Teleimpedance and Tactile Feedback for Intuitive Control of the Pisa/IIT SoftHand

This paper proposes a teleimpedance controller with tactile feedback for more intuitive control of the Pisa/IIT SoftHand. With the aim to realize a robust, efficient and low-cost hand prosthesis design, the SoftHand is developed based on the motor control principle of synergies, through which the immense complexity of the hand is simplified into distinct motor patterns. Due to the built-in flexibility of the hand joints, as the SoftHand grasps, it follows a synergistic path while allowing grasping of objects of various shapes using only a single motor. The DC motor of the hand incorporates a novel teleimpedance control in which the users postural and stiffness synergy references are tracked in real-time. In addition, for intuitive control of the hand, two tactile interfaces are developed. The first interface (mechanotactile) exploits a disturbance observer which estimates the interaction forces in contact with the grasped object. Estimated interaction forces are then converted and applied to the upper arm of the user via a custom made pressure cuff. The second interface employs vibrotactile feedback based on surface irregularities and acceleration signals and is used to provide the user with information about the surface properties of the object as well as detection of object slippage while grasping. Grasp robustness and intuitiveness of hand control were evaluated in two sets of experiments. Results suggest that incorporating the aforementioned haptic feedback strategies, together with user-driven compliance of the hand, facilitate execution of safe and stable grasps, while suggesting that a low-cost, robust hand employing hardware-based synergies might be a good alternative to traditional myoelectric prostheses.

A synergy-driven approach to a myoelectric hand

In this paper, we present the Pisa/IIT SoftHand with myoelectric control as a synergy-driven approach for a prosthetic hand. Commercially available myoelectric hands are more expensive, heavier, and less robust than their body-powered counterparts; however, they can offer greater freedom of motion and a more aesthetically pleasing appearance. The Pisa/IIT SoftHand is built on the motor control principle of synergies through which the immense complexity of the hand is simplified into distinct motor patterns. As the SoftHand grasps, it follows a synergistic path with built-in flexibility to allow grasping of a wide variety of objects with a single motor. Here we test, as a proof-of-concept, 4 myoelectric controllers: a standard controller in which the EMG signal is used only as a position reference, an impedance controller that determines both position and stiffness references from the EMG input, a standard controller with vibrotactile force feedback, and finally a combined vibrotactile-impedance (VI) controller. Four healthy subjects tested the control algorithms by grasping various objects. All controllers were sufficient for basic grasping, however the impedance and vibrotactile controllers reduced the physical and cognitive load on the user, while the combined VI mode was the easiest to use of the four. While these results need to be validated with amputees, they suggest a low-cost, robust hand employing hardware-based synergies is a viable alternative to traditional myoelectric prostheses.

Teleimpedance control of a synergy-driven anthropomorphic hand

In this paper, a novel synergy driven teleimpedance controller for the Pisa-IIT SoftHand is presented. Towards the development of an efficient, robust, and low-cost hand prothesis, the Pisa-IIT SoftHand is built on the motor control principle of synergies, through which the immense complexity of the hand is simplified into distinct motor patterns. As the SoftHand grasps, it follows a synergistic path with built-in flexibility to allow grasping of objects of various shapes using only a single motor. In this work, the hand grasping motion is regulated with an impedance controller which incorporates the users postural and stiffness synergy profiles in realtime. In addition, a disturbance observer is realized which estimates the grasping contact force. The estimated force is then fedback to the user via a vibration motor. Grasp robustness and transparency improvements were evaluated on two healthy subjects while grasping different objects. Implementation of the proposed teleimpedance controller led to the execution of stable grasps by controlling the grasping forces, via modulation of hand compliance. In addition, utilization of the vibrotactile feedback resulted in reduced physical load on the user. While these results need to be validated with amputees, they provide evidence that a low-cost, robust hand employing hardware-based synergies is a viable alternative to traditional myoelectric prostheses.

Hand function recovery in chronic stroke with HEXORR robotic training: A case series

After a stroke, many survivors have impaired motor function. Robotic rehabilitation techniques have emerged to provide a repetitive, activity-based therapy at potentially lower cost than conventional methods. Many patients exhibit intrinsic resistance to hand extension in the form of spasticity and/or hypertonia. We have developed a therapy program using the Hand Exoskeleton Rehabilitation Robot (HEXORR) that is capable of compensating for tone to assist patients in opening the paretic hand. The system can move the users hand, assist movement, allow free movement, or restrict movement to allow static force production. These options combine with an interactive virtual reality game to enhance user motivation. Four chronic stroke subjects received 18 sessions of robot therapy as well as pre and post evaluation sessions. All subjects showed at least modest gains in active finger range of motion (ROM) measured in the robot, and all but one subject had gains in active thumb ROM. Most of these gains carried over to ROM gains outside of the robot. The clinical measures (Fugl-Meyer, Box-and-Blocks) showed clear improvements in two subjects and mixed results in two subjects. Overall, the robot therapy was well received by subjects and shows promising results. We conclude HEXORR therapy is best suited for patients with mild-moderate tone and at least minimal extension.

Cortical effects of repetitive finger flexion- vs. extension-resisted tracking movements: a TMS study

While the cortical effects of repetitive motor activity are generally believed to be task specific, the task parameters that modulate these effects are incompletely understood. Since there are differences in the neural control of flexor vs. extensor muscles, the type of muscles involved in the motor task of interest may be one important parameter. In addition, the role each muscle plays in the task, such as whether or not it is the prime mover, is another potentially important task parameter. In the present study, use-dependent cortical plasticity was examined in healthy volunteers performing a robotic waveform tracking task with either the extensor digitorum communis (EDC) or flexor digitorum superficialis (FDS) acting as the prime mover. Transcranial magnetic stimulation was used to measure corticospinal excitability (CE) and short-interval intracortical inhibition of lower and higher threshold corticospinal neurons (SICI(L) and SICI(H), respectively) before and after a flexion- or extension-resisted finger tracking task. After repetitive performance of the tracking task, there was a significant decrease in SICI(L) targeting the EDC, while no change in CE targeting EDC was observed. In contrast, the reverse pattern was observed in the FDS: a significant increase in CE with no change in SICI(L). There was also a tendency toward increased SICI(H) targeting whichever muscle was acting as the prime mover, although this effect did not reach statistical significance. We conclude that there is a difference in patterns of use-dependent plasticity between extrinsic finger flexor and extensor muscles performing the same task.

Clinical effects of using HEXORR (Hand Exoskeleton Rehabilitation Robot) for movement therapy in stroke rehabilitation.

ObjectiveThe goals of this pilot study were to quantify the clinical benefits of using the Hand Exoskeleton Rehabilitation Robot for hand rehabilitation after stroke and to determine the population best served by this intervention. DesignNine subjects with chronic stroke (one excluded from analysis) completed 18 sessions of training with the Hand Exoskeleton Rehabilitation Robot and a preevaluation, a postevaluation, and a 90-day clinical evaluation. ResultsOverall, the subjects improved in both range of motion and clinical measures. Compared with the preevaluation, the subjects showed significant improvements in range of motion, grip strength, and the hand component of the Fugl-Meyer (mean changes, 6.60 degrees, 8.84 percentage points, and 1.86 points, respectively). A subgroup of six subjects exhibited lower tone and received a higher dosage of training. These subjects had significant gains in grip strength, the hand component of the Fugl-Meyer, and the Action Research Arm Test (mean changes, 8.42 percentage points, 2.17 points, and 2.33 points, respectively). ConclusionsFuture work is needed to better manage higher levels of hypertonia and provide more support to subjects with higher impairment levels; however, the current results support further study into the Hand Exoskeleton Rehabilitation Robot treatment.

The SoftHand Pro: Translation from Robotic Hand to Prosthetic Prototype

This work presents the translation from a humanoid robotic hand to a prosthetic prototype and its first evaluation in a set of 9 persons with amputation. The Pisa/IIT SoftHand is an underactuated hand built on the neuroscientific principle of motor synergies enabling it to perform natural, human-like movements and mold around grasped objects with minimal control input. These features motivated the development of the SoftHand Pro, a prosthetic version of the SoftHand built to interface with a prosthetic socket. The results of the preliminary testing of the SoftHand Pro showed it to be a highly functional design with an intuitive control system. Present results warrant further testing to develop the SoftHand Pro.

Influence of force feedback on grasp force modulation in prosthetic applications: A preliminary study

In typical movement, humans use a combination of feed-forward and feedback motor control strategies to interact with the world around them. However, when sensory input is impaired or absent, as in the case of various neuropathies or amputation, the ability to perform everyday tasks, like modulating grip force to object weight, can be affected. In this study, we show the results of a preliminary study using a pressure cuff-like force feedback device (CUFF) with the SoftHand Pro (SHP) prosthetic hand. Subjects lifted an object of various weights using their own hand, with the SHP without feedback, and the SHP with force feedback. As expected, significant differences were found between the two SHP conditions and the native hand, but surprisingly not between the SHP conditions. A closer look at the data suggests the feedback may help diminish the overall grip force used during grasping even if it does not alter the grip force modulation to object weight. The lack of significance may be due in part to high intra- and inter-subject variability. Additional training with the CUFF and/or customization of the feedback may enhance the effects and warrants further study.