A Trade-Off between Complexity and Interaction Quality for Upper Limb Exoskeleton Interfaces

Exoskeletons are among the most promising devices dedicated to assisting human movement during reeducation protocols and preventing musculoskeletal disorders at work. However, their potential is currently limited, partially because of a fundamental contradiction impacting their design. Indeed, increasing the interaction quality often requires the inclusion of passive degrees of freedom in the design of human-exoskeleton interfaces, which increases the exoskeleton's inertia and complexity. Thus, its control also becomes more complex, and unwanted interaction efforts can become important. In the present paper, we investigate the influence of two passive rotations in the forearm interface on sagittal plane reaching movements while keeping the arm interface unchanged (i.e., without passive degrees of freedom). Such a proposal represents a possible compromise between conflicting design constraints. The in-depth investigations carried out here in terms of interaction efforts, kinematics, electromyographic signals, and subjective feedback of participants all underscored the benefits of such a design. Therefore, the proposed compromise appears to be suitable for rehabilitation sessions, specific tasks at work, and future investigations into human movement using exoskeletons.

Model-Based Mid-Level Regulation for Assist-As-Needed Hierarchical Control of Wearable Robots: A Computational Study of Human-Robot Adaptation

The closed-loop human–robot system requires developing an effective robotic controller that considers models of both the human and the robot, as well as human adaptation to the robot. This paper develops a mid-level controller providing assist-as-needed (AAN) policies in a hierarchical control setting using two novel methods: model-based and fuzzy logic rule. The goal of AAN is to provide the required extra torque because of the robot’s dynamics and external load compared to the human limb free movement. The human–robot adaptation is simulated using a nonlinear model predictive controller (NMPC) as the human central nervous system (CNS) for three conditions of initial (the initial session of wearing the robot, without any previous experience), short-term (the entire first session, e.g., 45 min), and long-term experiences. The results showed that the two methods (model-based and fuzzy logic) outperform the traditional proportional method in providing AAN by considering distinctive human and robot models. Additionally, the CNS actuator model has difficulty in the initial experience and activates both antagonist and agonist muscles to reduce movement oscillations. In the long-term experience, the simulation shows no oscillation when the CNS NMPC learns the robot model and modifies its weights to simulate realistic human behavior. We found that the desired strength of the robot should be increased gradually to ignore unexpected human–robot interactions (e.g., robot vibration, human spasticity). The proposed mid-level controllers can be used for wearable assistive devices, exoskeletons, and rehabilitation robots.

Force and electromyography responses during isometric force release of different rates and step-down magnitudes

This study investigated motor responses of force release during isometric elbow flexion by comparing effects of different ramp durations and step-down magnitudes. Twelve right-handed participants (age: 23.1 ± 1.1) performed trajectory tracking tasks. Participants were instructed to release their force from the reference magnitude (REF; 40% of maximal voluntary contraction force) to a step-down magnitude of 67% REF or 33% REF and maintain the released magnitude. Force release was guided by ramp durations of either 1 s or 5 s. Electromyography of the biceps brachii and triceps brachii was performed during the experimental task, and the co-contraction ratio was evaluated. Force output was recorded to evaluate the parameters of motor performance, such as force variability and overshoot ratio. Although a longer ramp duration of 5 s decreased the force variability and overshoot ratio than did shorter ramp duration of 1 s, higher perceived exertion and co-contraction ratio were followed. Force variability was greater when force was released to the step-down magnitude of 33% REF than that when the magnitude was 67% REF, however, the overshoot ratio showed opposite results. This study provided evidence proving that motor control strategies adopted for force release were affected by both duration and step-down magnitude. In particular, it implies that different control strategies are required according to the level of step-down magnitude with a relatively short ramp duration.

Design and Kinematic Analysis of Co-Exoskeleton with Passive Translational Joints for Upper-Limb Rehabilitation

A key approach for reducing motor impairment and regaining independence after spinal cord injuries or strokes is frequent and repetitive functional training. A compatible exoskeleton (Co-Exoskeleton) with four passive translational joints is proposed for the upper-limb rehabilitation. There are only three passive translational joints to track and assist movements of the glenohumeral joint (GH), where two joints are installed horizontally at the front section and another one at the connecting interface of the upper arm. This type of configuration can lower the influences of gravities of the exoskeleton device and upper extremity. The kinematic models of GH and the corresponding human–machine system are established using the analytical method. A numerical simulation of the kinematic models is implemented with MATLAB to emphatically analyze the kinematic characteristics of passive joints and the center of Co-Exoskeleton. The translational displacements of passive joints in four elevation planes are obtained during the elevating process. The results of the kinematic analysis show that the passive joints have similar motion characteristics under different elevation planes. Additionally, the position changes of GH in three directions can be tracked and compensated approximately. Co-Exoskeleton has an especially good compensation effect for the vertical movement of GH. The compensation effect and kinematic models are verified by using the elevating experiments. This research provides theoretical and methodological guidance for the ergonomic design and kinematic analysis of the rehabilitation exoskeleton.

Empowering lower limbs exoskeletons: state-of-the-art

Given the advanced breakthroughs in the field of supportive robotic technologies, interest in the integration of the human body and a robot into a single system has rapidly increased. The aim of this work is to provide an overview of empowering lower limbs exoskeletons. Along with lower exoskeleton limbs, their unique design concepts, operator–exoskeleton interactions and control strategies are described. Although many problems have been solved in recent development, many challenges remain. Especially in the context of infantry soldiers, fire fighters and rescuers, the challenges of empowering exoskeletons are discussed, and improvements are outlined and described. This study is not only a summary of the current state, but also points to weaknesses of empowering lower limbs exoskeletons and outlines possible improvements.

On the assessment of coordination between upper extremities: towards a common language between rehabilitation engineers, clinicians and neuroscientists

Well-developed coordination of the upper extremities is critical for function in everyday life. Interlimb coordination is an intuitive, yet subjective concept that refers to spatio-temporal relationships between kinematic, kinetic and physiological variables of two or more limbs executing a motor task with a common goal. While both the clinical and neuroscience communities agree on the relevance of assessing and quantifying interlimb coordination, rehabilitation engineers struggle to translate the knowledge and needs of clinicians and neuroscientists into technological devices for the impaired. The use of ambiguous definitions in the scientific literature, and lack of common agreement on what should be measured, present large barriers to advancements in this area. Here, we present the different definitions and approaches to assess and quantify interlimb coordination in the clinic, in motor control studies, and by state-of-the-art robotic devices. We then propose a taxonomy of interlimb activities and give recommendations for future neuroscience-based robotic- and sensor-based assessments of upper limb function that are applicable to the everyday clinical practice. We believe this is the first step towards our long-term goal of unifying different fields and help the generation of more consistent and effective tools for neurorehabilitation.

Analytical Inverse Kinematic Resolution of a Redundant Exoskeleton for Upper-Limb Rehabilitation

Robot-assisted therapy has played a significant role in helping the disabled patients to restore motor functions. In this paper, a redundant exoskeleton is developed for upper-limb rehabilitation. An analytical methodology for obtaining the inverse kinematic solution of the exoskeleton is presented to provide synchronized movement with patients and ensure natural human–robot interaction. To mathematically express the redundancy problem, the swivel angle of elbow is introduced as an additional parameter to specify the human arm congratulation with a predefined wrist location. A kinematic criterion is proposed to determine the swivel angle by imitating the natural reflexive reaction of human arm. The effectiveness of the proposed strategy is experimentally evaluated via four representative types of upper-limb motion tasks. During the experiments, the actual kinematic data of human arm is collected by utilizing an articulated motion capture system integrated with inertial sensors and, after that, compared to the estimation results generated by the proposed redundancy resolution. The experimental results indicate that the kinematic criterion of swivel angle is suitable to describe the free reaching movement without additional constraints. Moreover, with the estimated swivel angles, the root mean square errors between the actual and calculated joint angles are normally less than 8[Formula: see text].

Bilateral robots for upper-limb stroke rehabilitation: State of the art and future prospects

Robot-assisted bilateral upper-limb training grows abundantly for stroke rehabilitation in recent years and an increasing number of devices and robots have been developed. This paper aims to provide a systematic overview and evaluation of existing bilateral upper-limb rehabilitation devices and robots based on their mechanisms and clinical-outcomes. Most of the articles studied here were searched from nine online databases and the China National Knowledge Infrastructure (CNKI) from year 1993 to 2015. Devices and robots were categorized as end-effectors, exoskeletons and industrial robots. Totally ten end-effectors, one exoskeleton and one industrial robot were evaluated in terms of their mechanical characteristics, degrees of freedom (DOF), supported control modes, clinical applicability and outcomes. Preliminary clinical results of these studies showed that all participants could gain certain improvements in terms of range of motion, strength or physical function after training. Only four studies supported that bilateral training was better than unilateral training. However, most of clinical results cannot definitely verify the effectiveness of mechanisms and clinical protocols used in robotic therapies. To explore the actual value of these robots and devices, further research on ingenious mechanisms, dose-matched clinical protocols and universal evaluation criteria should be conducted in the future.

Walking Gait of a Biped with a Wearable Walking Assist Device

A ballistic walking gait is designed for a planar biped equipped with a wearable walking assist device. The biped is a seven-link planar biped with two legs, two feet, and a trunk. The wearable walking assist device is composed of a bodyweight support, two upper legs, two lower legs, and two shoes. The dynamic model of the biped with its walking assist device, containing two closed kinematic chains, is calculated by virtually cutting each of both loops at one of their point. In the single support phase, the biped with its assist device moves due to the existence of a momentum, produced mechanically, without applying active torques in the inter-link joints. The biped and this assist device are controlled with impulsive torques at the instantaneous double support to obtain a cyclic gait. The impulsive torques are applied in the six inter-link joints of the biped and in several inter-link joints of the wearable walking assist device. The following distributions of impulsive torques, in the knees or the ankles, hips and knees, hips and ankles, or knees and ankles and the fully assist device, are compared with the case of no assistance for the biped. Each time, an infinity of solutions exists to find the impulsive torques. An energy cost functional defined from these impulsive torques is minimized to determine a unique solution. Numerical results show that for a given time period and a given length of the walking gait step, the assistance of the hips is a good compromise to help the biped.

Robotic Rehabilitation Game Design for Chronic Stroke

OBJECTIVE

This study investigates games intended for use with an upper-limb exoskeleton robot operated unilaterally and bilaterally. Games are evaluated in terms of usability and preference for stroke survivors. Game design considerations relating to the human to machine interface, are also discussed.

SUBJECTS AND METHODS

Ten hemiparetic stroke survivors completed 12 90-minute sessions using an upper-limb robotic exoskeleton unilaterally and bilaterally. During the sessions subjects played seven different games designed for rehabilitation. At the conclusion of their sessions subjects completed an 83-question survey.

RESULTS

Subjects preferred static games to dynamic games. Preferred games elicited greater effort.

CONCLUSIONS

Intermediate goals in addition to ultimate goals should be set with both static and dynamic games such that even with the patient's limited range of motion, speed, or coordination, the game should be playable and provide a sense of accomplishment to the patient. Marking the games' ultimate goals that can be accomplished only by healthy subjects, such as range of motion and workspace, provide references and encouragement to the patient for improving motor control and performance through the process of playing the game.

Fuzzy Sliding Mode Control of a Multi-DOF Parallel Robot in Rehabilitation Environment

Multi-degrees of freedom (DOF) parallel robot, due to its compact structure and high operation accuracy, is a promising candidate for medical rehabilitation devices. However, its controllability relating to the nonlinear characteristics challenges its interaction with human subjects during the rehabilitation process. In this paper, we investigated the control of a parallel robot system using fuzzy sliding mode control (FSMC) for constructing a simple controller in practical rehabilitation, where a fuzzy logic system was used as the additional compensator to the sliding mode controller (SMC) for performance enhancement and chattering elimination. The system stability is guaranteed by the Lyapunov stability theorem. Experiments were conducted on a lower limb rehabilitation robot, which was built based on kinematics and dynamics analysis of the 6-DOF Stewart platform. The experimental results showed that the position tracking precision of the proposed FSMC is sufficient in practical applications, while the velocity chattering had been effectively reduced in comparison with the conventional FSMC with parameters tuned by fuzzy systems.

Kinematic analysis of upper extremity movement during drinking in hemiplegic subjects

BACKGROUND

It is necessary to analyze the kinematic properties of a paralyzed extremity to quantitatively determine the degree of impairment of hemiplegic people during functional activities of daily living (ADL) such as a drinking task. This study aimed to identify the kinematic differences between 16 hemiplegic and 32 able-bodied participants in relation to the task phases when drinking with a cup and the kinematic strategy used during motion with respect to the gravity direction.

METHODS

The subjects performed a drinking task that was divided into five phases according to Murphy's phase definition: reaching, forward transport, drinking, backward transport, and returning. We found that the groups differed in terms of the movement times and the joint angles and angular velocities of the shoulder, elbow, and wrist joints.

FINDINGS

Compared to the control group, the hemiplegic participants had a larger shoulder abduction angle of at most 17.1° during all the phases, a larger shoulder flexion angle of 7.6° during the reaching phase, and a smaller shoulder flexion angle of 6.4° during the backward transporting phase. Because of these shoulder joint patterns, a smaller elbow pronation peak angle of at most 13.1° and a larger wrist extension peak angle of 12.0° were found in the motions of the hemiplegic participants, as compensation to complete the drinking task. The movement in the gravity direction during the backward transporting phase resulted in a 15.9% larger peak angular velocity for elbow extension in the hemiplegic participants compared to that of the control group.

INTERPRETATION

These quantitative kinematic patterns help provide an understanding of the movements of an affected extremity and can be useful in designing rehabilitation robots to assist hemiplegic people with ADL.

A task description model for robotic rehabilitation

The desire to produce robots to aid in physical neurorehabilitation has led to the control paradigm Assistance-As-Needed. This paradigm aims to assist patients in performing physical rehabilitation tasks whilst providing the least amount of assistance required, maximizing the patient's effort which is essential for recovery. Ideally the provided assistance equals the gap between the capability required to perform the task and the patient's available capability. Current implementations derive a measure of this gap by critiquing task performance based on some criteria. This paper presents a task description model for tasks performed by a patient's limb, allowing physical requirements to be calculated. Applied to two upper limb tasks typical of rehabilitation and daily activities, the effect of task variations on the task's physical requirements are observed. It is proposed that using the task description model to compensate for changing task requirements will allow better support by providing assistance closer to the true needs of the patient.

Exoskeleton Technology in Rehabilitation: Towards an EMG-Based Orthosis System for Upper Limb Neuromotor Rehabilitation

The rehabilitation of patients should not only be limited to the first phases during intense hospital care but also support and therapy should be guaranteed in later stages, especially during daily life activities if the patient’s state requires this. However, aid should only be given to the patient if needed and as much as it is required. To allow this, automatic self-initiated movement support and patient-cooperative control strategies have to be developed and integrated into assistive systems. In this work, we first give an overview of different kinds of neuromuscular diseases, review different forms of therapy, and explain possible fields of rehabilitation and benefits of robotic aided rehabilitation. Next, the mechanical design and control scheme of an upper limb orthosis for rehabilitation are presented. Two control models for the orthosis are explained which compute the triggering function and the level of assistance provided by the device. As input to the model fused sensor data from the orthosis and physiology data in terms of electromyography (EMG) signals are used.

A systematic review of bilateral upper limb training devices for poststroke rehabilitation

Introduction. In stroke rehabilitation, bilateral upper limb training is gaining ground. As a result, a growing number of mechanical and robotic bilateral upper limb training devices have been proposed. Objective. To provide an overview and qualitative evaluation of the clinical applicability of bilateral upper limb training devices. Methods. Potentially relevant literature was searched in the PubMed, Web of Science, and Google Scholar databases from 1990 onwards. Devices were categorized as mechanical or robotic (according to the PubMed MeSH term of robotics). Results. In total, 6 mechanical and 14 robotic bilateral upper limb training devices were evaluated in terms of mechanical and electromechanical characteristics, supported movement patterns, targeted part and active involvement of the upper limb, training protocols, outcomes of clinical trials, and commercial availability. Conclusion. Initial clinical results are not yet of such caliber that the devices in question and the concepts on which they are based are firmly established. However, the clinical outcomes do not rule out the possibility that the concept of bilateral training and the accompanied devices may provide a useful extension of currently available forms of therapy. To actually demonstrate their (surplus) value, more research with adequate experimental, dose-matched designs, and sufficient statistical power are required.

Redundancy resolution of a human arm for controlling a seven DOF wearable robotic system

The human arm including the shoulder, elbow, wrist joints and exclusion scapular motion has 7 Degrees of Freedom (DOF) while positioning of the wrist in space and orientating the palm is a task that requires 6 DOF. As such it includes one more DOF than is needed to complete the task. Given the redundant nature of the arm, multiple arm configurations can be used to complete a task, which is expressed mathematically by none unique solution for the inverse kinematics. Despite this mathematical difficulty, the motor control provides a unique solution for the arm redundancy as the arm is moved in space. Resolving this redundancy is becoming critical as the human interacts with a wearable robotic system(exoskeleton) which includes the same redundancy as the human arm. Therefore, the inverse kinematics solution resolving the redundancy of these two coupled systems must be identical in order to guarantee a seamless integration. The redundancy of the arm can be formulated kinematically by defining the swivel angle - the rotation angle of the plane including the upper and lower arm around a virtual axis connecting the shoulder and wrist joints which are fixed in space. Analyzing reaching tasks recorded with a motion capture lab indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points the head. Based on these experimental results, selecting the point around the center of the head as a stationary target allows to calculate the swivel angle and in that way to resolve the human arm redundancy. Experimental results indicated that by using the proposed redundancy resolution criteria the error between the predicted swivel angle and the actual swivel angle adopted by the motor control system is less then 5 Deg. This criterion or a synthesis of several additional criteria may improve the synergistic relationships between an operator and a wearable robotic system.

Redundancy resolution of the human arm and an upper limb exoskeleton

The human arm has 7 degrees of freedom (DOF) while only 6 DOF are required to position the wrist and orient the palm. Thus, the inverse kinematics of an human arm has a nonunique solution. Resolving this redundancy becomes critical as the human interacts with a wearable robot and the inverse kinematics solution of these two coupled systems must be identical to guarantee an seamless integration. The redundancy of the arm can be formulated by defining the swivel angle, the rotation angle of the plane defined by the upper and lower arm around a virtual axis that connects the shoulder and wrist joints. Analyzing reaching tasks recorded with a motion capture system indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points to the head. Based on these experimental results, a new criterion is formed to resolve the human arm redundancy. This criterion was implemented into the control algorithm of an upper limb 7-DOF wearable robot. Experimental results indicate that by using the proposed redundancy resolution criterion, the error between the predicted and the actual swivel angle adopted by the motor control system is less then 5°.

Redundancy and joint limits of a seven degree of freedom upper limb exoskeleton

The seven degree of freedom arm model is widely used in robotics, computer graphics, and much more. For wearable robotic systems, which are subject to joint limits, it is desirable to relate the joint limits to the redundantly of the system. A brief review of the arm model, redundant space and kinematics is presented. Following this review a closed form method is developed calculate the interval of the swivel angle (which characterizes the redundancy) that produces arm configurations that stay within joint limits.

Viscoelastic model for redundancy resolution of the human arm via the swivel angle: applications for upper limb exoskeleton control

One of the key research efforts associated with a redundant seven degree of freedom (7-DOF) upper limb exoskeleton robot that is mechanically coupled to the human body is to develop high and low level control algorithms that enable the system to become a natural extension of the human body. Improving the synergistic relationship between the exoskeleton and the operator is manifested in part by decreasing the force exchange between the two entities. Such a reduction is accomplished in part by developing criteria for resolving the human arm redundancy. The redundancy may be represented by a swivel angle which is defined as the angular rotation of the elbow around an axis that passes through the shoulder and wrist joints. The proposed criteria for defining the swivel angle takes into account the dynamics of the human arm along with a viscoelastic muscle-like model with variable damping. The swivel angle is estimated using the pseudo-inverse of the Jacobian with a secondary objective function that estimates the desired joint angles during human arm movement. The result is then fed to the muscle model to create a more realistic human motion. The estimated swivel angle is then compared with the actual swivel angle measured experimentally by a motion capture system. Results indicate that the average error between the estimated and measured swivel joint angle is 4.4 degrees (in the range [3.7-6] degrees), which are lower than the kinematically based redundant resolution criterion.

Medical Robots: Current Systems and Research Directions

First used medically in 1985, robots now make an impact in laparoscopy, neurosurgery, orthopedic surgery, emergency response, and various other medical disciplines. This paper provides a review of medical robot history and surveys the capabilities of current medical robot systems, primarily focusing on commercially available systems while covering a few prominent research projects. By examining robotic systems across time and disciplines, trends are discernible that imply future capabilities of medical robots, for example, increased usage of intraoperative images, improved robot arm design, and haptic feedback to guide the surgeon.

Effective Game use in Neurorehabilitation

Games possess highly favourable attributes to bring to the field of neurorehabilitation by means of providing motivation and goal-directed exercise tasks. For the use of games to be effectively integrated in the commercial and clinical rehabilitation marketplace, it is necessary that a unified and comprehensive rehabilitation gaming platform be developed following principles of user-centered design. The needed platform must contain compatible modules for the planning and execution of treatment as well as progress assessment, and its development must take into consideration the needs and viewpoints of the involved stakeholders and the required supporting factors, including: patient, prescriber, therapist, care-provider, family, clinic, as well as supporting scientific evidence, technology, and policy. A proposed platform and needed components are explained and an example prototype rehabilitation platform is provided for discussion.

Implantable myoelectric sensors (IMESs) for intramuscular electromyogram recording

We have developed a multichannel electrogmyography sensor system capable of receiving and processing signals from up to 32 implanted myoelectric sensors (IMES). The appeal of implanted sensors for myoelectric control is that electromyography (EMG) signals can be measured at their source providing relatively cross-talk-free signals that can be treated as independent control sites. An external telemetry controller receives telemetry sent over a transcutaneous magnetic link by the implanted electrodes. The same link provides power and commands to the implanted electrodes. Wireless telemetry of EMG signals from sensors implanted in the residual musculature eliminates the problems associated with percutaneous wires, such as infection, breakage, and marsupialization. Each implantable sensor consists of a custom-designed application-specified integrated circuit that is packaged into a biocompatible RF BION capsule from the Alfred E. Mann Foundation. Implants are designed for permanent long-term implantation with no servicing requirements. We have a fully operational system. The system has been tested in animals. Implants have been chronically implanted in the legs of three cats and are still completely operational four months after implantation.