Effects of Impedance Reduction of a Robot for Wrist Rehabilitation on Human Motor Strategies in Healthy Subjects during Pointing Tasks

Studies on human motor control demonstrated the existence of simplifying strategies (namely `Donders' law') adopted to deal with kinematically redundant motor tasks. In recent research we showed that Donders' law also holds for human wrist during pointing tasks, and that it is heavily perturbed when interacting with a highly back-drivable state-of-the-art rehabilitation robot. We hypothesized that this depends on the excessive mechanical impedance of the Pronation/Supination (PS) joint of the robot and in this work we analyzed the effects of its reduction. To this end we deployed a basic force control scheme, which minimizes human-robot interaction force. This resulted in a 70% reduction of the inertia in PS joint and in decrease of 81% and 78% of the interaction torques during 1-DOF and 3-DOFs tasks. To assess the effects on human motor strategies, pointing tasks were performed by three subjects with a lightweight handheld device, interacting with the robot using its standard PD control (setting impedance to zero) and with the force-controlled robot. We quantified Donders' law as 2-dimensional surfaces in the 3-dimensional configuration space of rotations. Results revealed that the subject-specific features of Donders' surfaces reappeared after the reduction of robot impedance obtained via the force control

Design and Characterization of a Novel High-Power Series Elastic Actuator for a Lower Limb Robotic Orthosis

A safe interaction is crucial in wearable robotics in general, while in assistive and rehabilitation applications, robots may also be required to minimally perturb physiological movements, ideally acting as perfectly transparent machines. The actuation system plays a central role because the expected performance, in terms of torque, speed and control bandwidth, must not be achieved at the expense of lightness and compactness. Actuators embedding compliant elements, such as series elastic actuators, can be designed to meet the above-mentioned requirements in terms of high energy storing capacity and stability of torque control. A number of series elastic actuators have been proposed over the past 20 years in order to accommodate the needs arising from specific applications. This paper presents a novel series elastic actuator intended for the actuation system of a lower limb wearable robot, recently developed in our lab. The actuator is able to deliver 300 W and has a novel architecture making its centre of mass not co-located with its axis of rotation, for an easier integration into the robotic structure. A custom-made torsion spring with a stiffness of 272.25 N·m·rad– 1 is directly connected to the load. The delivered torque is calculated from the measurement of the spring deflection, through two absolute encoders. Testing on torque measurement accuracy and torque/stiffness control are reported

Analysis of Hand Intra-Finger Couplings During Flexion Movements in the Free Space

The anatomy of the human hand is characterized by intrinsic coupling mechanisms at the level of the tendons and bone structure. The intra-finger constraints, in particular, represent coupled movements of the joints of the same finger. Previous studies verified the existence of intra-finger couplings for circular and prismatic grasps, and hypothesized the existence of such couplings for free flexion-extension movements of the fingers without, however, quantifying them. The aim of this work was: i) to calculate subject-specific intra-finger couplings during flexion movements in the free space by exploiting a marker-based motion capture system and a validated kinematic protocol to guarantee high accuracy of the reconstructed hand kinematics, ii) to understand the effect of the hand size and of the finger on the coupling relations, and iii) to establish generalized coupling coefficients that could be used to simplify the kinematic hand model. To this purpose, ten healthy subjects performed flexion-extension movements of the fingers. Subject-specific couplings were extracted through linear regression analysis on pairs of adjacent joint angle trajectories: proximal couplings represented the relation between the Proximal-Inter-Phalangeal and MetaCarpo-Phalangeal joints for the long fingers and between the MetaCarpo-Phalangeal and Carpo-MetaCarpal joints for the thumb, whereas distal couplings represented the relation between the Distal-Inter-Phalangeal and Proximal-Inter-Phalangeal joints for the long fingers and between Inter-Phalangeal and MetaCarpo-Phalangeal joints for the thumb. The subject-specific coupling coefficients were independent from the hand size, and a difference between the distal couplings of the thumb and of the index, middle and ring fingers was highlighted. Regression analysis on the average flexion trajectories calculated on the ten participants showed a linear trend for both proximal and distal couplings ( R^{2}>0.97 ) and small Root Mean Square Errors (1.63 deg on average). Coupling coefficients ranged 1.4 – 1.9 and 0.7 – 0.9 for the proximal and distal couplings respectively. Given its distinctive kinematic structure, the thumb exhibited a particular behaviour, as its proximal and distal couplings were the same. The extracted couplings represent normative coupling values on a population of ten individuals. The obtained results suggest the possibility of simplifying the kinematic hand model by imposing linear relations between the joints of each finger, thus reducing the number of independent degrees of freedom to one for each finger. This could be used to define input design parameters for the development of biomimetic hand prostheses and exoskeletons

Assessment of lower limbs kinematics during human–robot interaction using inertial measurement units

Introduction: The kinematic structure of wearable robots designed for lower limb rehabilitation usually replicates that of the human body (anthropomorphism), thus kinematic incompatibilities may arise from the mismatch between robotic and human joint axes of rotation. Conversely, non-anthropomorphic structures can be designed to be robust against misalignments, thus minimizing undesired interaction forces [1]. A non-anthropomorphic treadmill-based robot for hip and knee flexion/extension assistance, using compliant actuators [2] and deriving human joint kinematic patterns with forward kinematics, has been previously presented [3] and [4]. Inaccuracies in the mapping of rotations from the robot joint space to the human joint space may arise from: (1) human segments length estimation errors, which affect the human–robot parallel kinematic chain, (2) non-rigid human–robot connections and (3) uncertainty associated to the position of fastening points. The aim of this work is to validate the human joints kinematics estimated by the robot (RK) using that provided by inertial measurement units (IK) as reference. Methods:Ahealthy subject (male, 28 y.o.) walked on a treadmill at 0.55, 0.7 and 0.85 m/s wearing the robot. Four inertial measurement units (IMUs – Xsens, MTX, sampling frequency 50 Hz) were attached to the pelvis, thigh, and shank cuffs and to the foot on the right side (Fig. 1). The RK of hip and knee were estimated from the encoders measurements (sampling frequency 200 Hz) using the third-order polynomial approximation of the forward kinematic function derived in [3]. At the beginning of each trial, while the subject was standing (reference configuration), thigh and shank IMUs were mathematically aligned to the pelvis IMU. Hip and knee IK were estimated in terms of sagittal components of the relevant orientation vectors provided by the IMUs. Gait cycles were identified using the acceleration peaks at heel strike. Data from the encoders and IMUs were synchronized using an external trigger. The root mean square deviation (RMSD) between hip and knee RK and IK was computed for the three trials over 10 gait cycles. Results: Representative patterns of hip and knee angles in the sagittal plane (treadmill velocity: 0.55 m/s) are reported. RMSD values averaged over the three different gait speeds were 2.9±0.2◦ for the hip and 4.9±1.2◦ for the knee (mean±sd). In all the trials, maximum discrepancies were found at the peak values (RK peak extension angles were overestimated). Discussion: Non-anthropomorphic robots can offer several advantages in terms of wearability but they may introduce some inaccuracies in the estimation of human joints kinematics. However, results showed that hip and knee RK errors were within levels acceptable in the majority of clinical applications. Moreover, the systematic errors observed can be corrected through a proper calibration of the robot-to-human mapping. The estimate of lower limb kinematics from IMUs integrated in the robotic cuffs could facilitate the control of the robot

Technology-assisted balance assessment and rehabilitation in individuals with spinal cord injury: A systematic review

Balance is a crucial function of basic Activities of Daily Living (ADL) and is often considered the priority in Spinal Cord Injury (SCI) patients' rehabilitation. Technological devices have been developed to support balance assessment and training, ensuring an earlier, intensive, and goal-oriented motor therapy

Switching assistance for exoskeletons during cyclic motions

This paper proposes a novel control algorithm for torque-controlled exoskeletons assisting cyclic movements. The control strategy is based on the injection of energy parcels into the human-robot system with a timing that minimizes perturbations, i.e., when the angular momentum is maximum. Electromyographic activity of main flexor-extensor knee muscles showed that the proposed controller mostly favors extensor muscles during extension, with a statistically significant reduction in muscular activity in the range of 10–20% in 60 out of 72 trials (i.e., 83%), while no effect related to swinging speed was recorded (speed variation was lower than 10% in 92% of the trials). In the remaining cases muscular activity increment, when statistically significant, was less than 10%. These results showed that the proposed algorithm reduced muscular effort during the most energetically demanding part of the movement (the extension of the knee against gravity) without perturbing the spatio-temporal characteristics of the task and making it particularly suitable for application in exoskeleton-assisted cyclic motions.Published versio

Nursing-engineering interdisciplinary research: A synthesis of methodological approach to perform healthcare-technology integrated projects

In the dynamic landscape of contemporary healthcare, the imperative for advancing the frontiers of knowledge and improving patient outcomes necessitates a paradigm shift towards a multidisciplinary approach. This background great enhances a nurse's ability to interface with technology and create technical solutions such as robots, patient care devices, or computer simulation for patient care needs and nursing care delivery. This study aims to describe, through a narrative review of evidence, a methodology to develop and manager Nursing-Engineering interdisciplinary project, clarify the key points and facilitate professionals who are not very familiar with this topic. The methodology employed highlights the importance of this kind of research that allows to achieve highest standards of practice leading to improved patient care, innovative solutions and a global contribution to healthcare excellence

Improving the Standing Balance of Paraplegics through the Use of a Wearable Exoskeleton

In this study, our goal was to improve the standing balance of people with a spinal cord injury by using a wearable exoskeleton that has ankle and knee actuation in the sagittal plane. Three test-pilots that have an incomplete spinal cord injury wore the exoskeleton and tried to maintain standing balance without stepping while receiving anteroposterior pushes. Two balance controllers were tested: One providing assistance based on the subject's body sway and one based on the whole body momentum. For both controllers, the balance performances of the test-pilots wearing the exoskeleton were assessed based on the center of mass kinematics and compared to the condition in which the device did not provide any assistance. One of the test-pilots was not able to maintain balance without assistance, but could withstand small pushes when any of the balance controllers was implemented. For this test-pilot the recovery time and sway amplitude hardly varied with the type of balance controller that was used. For the other two test-pilots the recovery time and the sway amplitude were smallest using the body sway controller. In conclusion, the wearable exoskeleton with balance controller was able to improve the balance performance of the test-pilots by reducing the recovery time after a perturbation and by enabling one of the test-pilots to maintain balance, who could not maintain balance by himself