Arm Exoskeleton Research Articles

Sliding Mode Control with Model-Based Switching Functions applied on a 7-DOF Exoskeleton Arm

This article features a novel sliding mode controller for robotic arms using nonlinear model-based switching functions. The new controller is experimentally validated on a 7-DOF exoskeleton arm used for upper-limb rehabilitation applications. The proposed approach features a novel concept using model-based switching functions in the sliding mode controller, which leads to considerable simplifications on the torque control inputs. Compared to conventional linear switching functions, model-based switching functions show substantial control performance improvements on the torque inputs, such as transient constraints reduction and enhanced robustness, while maintaining a very good tracking performance. Moreover, model-based switching functions design ensures a complete decoupling of chattering effect between joint axes. Furthermore, this approach can be combined with existing chattering reduction techniques to ensure proper control of chattering levels on the torque inputs. These advantages make the practical implementation of the model-based switching functions approach particularly desirable for wearable robotics, where smooth movements and high accuracy are important requirements for patients’ comfort and security.

Design and Implement an Exoskeleton Arm for Reinforcement the Human Muscles after Stroke

Mobility limitations in stroke survivors yield negative impacts on the quality of life for such individuals. Rehabilitation is needed to help them recover and regain mobility. Accordingly, this study aims to design and validate a “Robotic Exoskeleton” intended for stroke rehabilitation. The basic principles of this robotic exoskeleton device are its dependence on electromyography signal and electronic microcontroller to provide an efficient physiotherapy exercises system.The robotic exoskeleton is a one degree of freedom which performs the flexion and extension of the elbow joint. After the design was completed, 19 subjects participated in this study: 4 healthy subjects, and 15 post-stroke patients.The results showed the benefit of robotic exoskeleton in increasing the elbow range of motion, where angle of elbow flexion was raised from the first physiotherapy session to maximum elbow flexion in the last session.

Object-oriented Changes in Hand Kinematics and Postural Sway of an Infant Wearing an Arm Exoskeleton

Object-oriented Changes in Hand Kinematics and Postural Sway of an Infant Wearing an Arm Exoskeleton

A light-weight passive upper arm assistive exoskeleton based on multi-linkage spring-energy dissipation mechanism for overhead tasks

This paper introduces a novel passive type upper arm exoskeletal vest for assisting overhead jobs in industrial environment such as automotive manufacturing centers. The developed upper arm exoskeleton named as Hyundai Vest Exoskeleton (H-VEX) proposes two key mechanical structural elements: (1) an energy-storage multi-linkage mechanism dissipating spring-loaded energy according to angle-increment of a wearer’s upper arm, and (2) a poly-centric shoulder joint mechanism on the transverse plane for its proper alignment with a wearer’s shoulder joint movement. Based on the proposed mechanical structures, H-VEX has effective ergonomic properties which enable it to provide a smooth-increasing upper arm assistive torque according to increment in a wearer’s arm angle up to its target angle without impeding movements in large ranges of motion (RoM). Especially, the critical design parameters of the energy-storage multi-linkage are able to be adjusted to generate customized assistive torque responses, and additionally, this mechanism can be covered in a thin cover frame for beneficial ergonomic & cosmetic reasons. Furthermore, industrial-purposed requirements such as mechanical endurance and cost-effectiveness can be achieved taking advantages of key structures.To verify the effectiveness of H-VEX on overhead works, activation signals of electromyography (EMG) on main corresponding muscles of ten subjects carrying out overhead manipulation tasks were measured and compared with cases without wearing the exoskeletal vest. The statistical analysis on acquired EMG signal indicates that assistive torque provided by H-VEX was shown to significantly decrease activation of the shoulder-related muscles during target tasks.

Robust Adaptive Tracking Control of Uncertain Rehabilitation Exoskeleton Robot

Abstract Rehabilitation robots have become an influential tool in physiotherapy treatment because they are able to provide intensive rehabilitation treatment over a long period of time. However, this technology still suffers from various problems such as dynamic uncertainties, external disturbances, and human–robot interaction. In this paper, we propose a robust adaptive control approach of an exoskeleton robot with an unknown dynamic model and external disturbances. First, the dynamics of the exoskeleton's arm is presented. Then, we design a robust adaptive sliding mode control in which the parameter uncertainties and the disturbances are estimated by the adaptive update methods. The proposed control ensures a good tracking of the system with a finite time convergence of sliding surface to zero. Throughout this paper, the designed control law and the global stability analysis are formulated and demonstrated based on the appropriate choice of the candidate Lyapunov function. The experimental and comparative results, performed for seven degrees-of-freedom (DOFs) exoskeleton arm with three healthy subjects to track a passive rehabilitation motion, confirm the effectiveness and robustness of the proposed control law compared with conventional adaptive approach.

Optimized Proportional-Integral-Derivative Controller for Upper Limb Rehabilitation Robot

This paper proposes a nature inspired, meta-heuristic optimization technique to tune a proportional-integral-derivative (PID) controller for a robotic arm exoskeleton RAX-1. The RAX-1 is a two-degrees-of-freedom (2-DOFs) upper limb rehabilitation robotic system comprising two joints to facilitate shoulder joint movements. The conventional tuning of PID controllers using Ziegler-Nichols produces large overshoots which is not desirable for rehabilitation applications. To address this issue, nature inspired algorithms have recently been proposed to improve the performance of PID controllers. In this study, a 2-DOF PID control system is optimized offline using particle swarm optimization (PSO) and artificial bee colony (ABC). To validate the effectiveness of the proposed ABC-PID method, several simulations were carried out comparing the ABC-PID controller with the PSO-PID and a classical PID controller tuned using the Zeigler-Nichols method. Various investigations, such as determining system performance with respect to maximum overshoot, rise and settling time and using maximum sensitivity function under disturbance, were carried out. The results of the investigations show that the ABC-PID is more robust and outperforms other tuning techniques, and demonstrate the effective response of the proposed technique for a robotic manipulator. Furthermore, the ABC-PID controller is implemented on the hardware setup of RAX-1 and the response during exercise showed minute overshoot with lower rise and settling times compared to PSO and Zeigler-Nichols-based controllers.

Assistive Arm-Exoskeleton Control Based on Human Muscular Manipulability.

This paper introduces a novel control framework for an arm exoskeleton that takes into account force of the human arm. In contrast to the conventional exoskeleton controllers where the assistance is provided without considering the human arm biomechanical force manipulability properties, we propose a control approach based on the arm muscular manipulability. The proposed control framework essentially reshapes the anisotropic force manipulability into the endpoint force manipulability that is invariant with respect to the direction in the entire workspace of the arm. This allows users of the exoskeleton to perform tasks effectively in the whole range of the workspace, even in areas that are normally unsuitable due to the low force manipulability of the human arm. We evaluated the proposed control framework with real robot experiments where subjects wearing an arm exoskeleton were asked to move a weight between several locations. The results show that the proposed control framework does not affect the normal movement behavior of the users while effectively reduces user effort in the area of low manipulability. Particularly, the proposed approach augments the human arm force manipulability to execute tasks equally well in the entire workspace of the arm.

Kinematics and workspace analysis of a modified portable exoskeleton arm

In order to solve the problems such as small workspace, complicated mechanical structure and motion interferences of traditional exoskeleton arm, a modified exoskeleton mechanism is proposed by optimizing the angles between the shoulder joint axes. In this paper, the model of traditional exoskeleton arm and the modified one are both built. And the kinematic theory of the two models is analysed and discussed. Furthermore, the Monte Carlo method is used to simulate the workspace of the mechanism with the help of the Matlab software. The simulation results show that the modified exoskeleton arm has larger workspace than the traditional one. So it can better meet the needs of more application scenarios.

Haptics control of an arm exoskeleton for virtual reality using PSO-based fixed structure H∞ control

This article proposes a robust haptics control algorithm for an arm exoskeleton in virtual reality application that guarantees the robustness of the force displaying performance. The developed arm exoskeleton allows the user to sense the profile of virtual objects through joints at wrist, elbow, and shoulder. Forces exerted by the user are directly measured by load cells attached to the links, which are used to determine the corresponding velocity command based on virtual impedance. Due to the imperfection of modeling and the measurement noises from load cells and encoder quantization, the force displaying performance of the device tends to degrade with increasing oscillation, causing permanent damages to the device and user. To solve this problem, a Particle swarm optimization (PSO)-based fixed structure H∞ controller is proposed to control the developed arm exoskeleton. The control performance of the proposed controller is evaluated by both simulation and experiment. The results show that the proposed controller can achieve better tracking performance in comparison with proportional–integral–derivative controller in terms of less oscillation and fast response.

Compliant adaptive control of human upper-limb exoskeleton robot with unknown dynamics based on a Modified Function Approximation Technique (MFAT)

Rehabilitation robots have shown a high potential for improving the patients’ mobility, improving their functional movements and assisting in daily activities. However, this technology is still an emerging field and suffers from several challenges like compliance control and dynamic uncertain caused by the human–robot collaboration. The main challenge addressed in this paper is to ensure that the exoskeleton robot provides a suitable compliance control that allows it to cooperate perfectly with humans even if the dynamic model of the exoskeleton robot is uncertain. To achieve that, an adaptive tracking controller based on Modified Function Approximation Technique (FAT) is proposed to approximate the dynamic model of the exoskeleton robot. Unlike a conventional FAT, the required use of basis functions in estimations law of dynamic model and the acceleration feedback is eliminated in the proposed modified FAT. Additionally, the desired trajectory is designed based on the designer’s prediction of the motion intention of the human, using the Damped Least Square method in order to reduce the error between the actual position of the robot and the motion intention of the human which help the subject move the exoskeleton arm easily in active rehabilitation tasks. The stability analysis is formulated and demonstrated based on Lyapunov function. An experimental physiotherapy session and comparison study with a healthy subject was performed to test the effectiveness and robustness of the proposed adaptive control.

A Linear Approach to Optimize an EMG-Driven Neuromusculoskeletal Model for Movement Intention Detection in Myo-Control: A Case Study on Shoulder and Elbow Joints.

The growing interest of the industry production in wearable robots for assistance and rehabilitation purposes opens the challenge for developing intuitive and natural control strategies. Myoelectric control, or myo-control, which consists in decoding the human motor intent from muscular activity and its mapping into control outputs, represents a natural way to establish an intimate human-machine connection. In this field, model based myo-control schemes (e.g., EMG-driven neuromusculoskeletal models, NMS) represent a valid solution for estimating the moments of the human joints. However, a model optimization is needed to adjust the model's parameters to a specific subject and most of the optimization approaches presented in literature consider complex NMS models that are unsuitable for being used in a control paradigm since they suffer from long-lasting setup and optimization phases. In this work we present a minimal NMS model for predicting the elbow and shoulder torques and we compare two optimization approaches: a linear optimization method (LO) and a non-linear method based on a genetic algorithm (GA). The LO optimizes only one parameter per muscle, whereas the GA-based approach performs a deep customization of the muscle model, adjusting 12 parameters per muscle. EMG and force data have been collected from 7 healthy subjects performing a set of exercises with an arm exoskeleton. Although both optimization methods substantially improved the performance of the raw model, the findings of the study suggest that the LO might be beneficial with respect to GA as the latter is much more computationally heavy and leads to minimal improvements with respect to the former. From the comparison between the two considered joints, it emerged also that the more accurate the NMS model is, the more effective a complex optimization procedure could be. Overall, the two optimized NMS models were able to predict the shoulder and elbow moments with a low error, thus demonstrating the potentiality for being used in an admittance-based myo-control scheme. Thanks to the low computational cost and to the short setup phase required for wearing and calibrating the system, obtained results are promising for being introduced in industrial or rehabilitation real time scenarios.

A High-Level Control Algorithm Based on sEMG Signalling for an Elbow Joint SMA Exoskeleton.

A high-level control algorithm capable of generating position and torque references from surface electromyography signals (sEMG) was designed. It was applied to a shape memory alloy (SMA)-actuated exoskeleton used in active rehabilitation therapies for elbow joints. The sEMG signals are filtered and normalized according to data collected online during the first seconds of a therapy session. The control algorithm uses the sEMG signals to promote active participation of patients during the therapy session. In order to generate the reference position pattern with good precision, the sEMG normalized signal is compared with a pressure sensor signal to detect the intention of each movement. The algorithm was tested in simulations and with healthy people for control of an elbow exoskeleton in flexion–extension movements. The results indicate that sEMG signals from elbow muscles, in combination with pressure sensors that measure arm–exoskeleton interaction, can be used as inputs for the control algorithm, which adapts the reference for exoskeleton movements according to a patient’s intention.

Hybrid robotic system combining passive exoskeleton and functional electrical stimulation for upper limb stroke rehabilitation: Preliminary results of the retrainer multi-center randomized controlled trial

Stroke is the main cause of acquired adult disability with major impact on arm function. The combined use of Functional Electrical Stimulation (FES) and robotic technologies is strongly advocated to improve rehabilitation outcomes after stroke. We present the preliminary data of a multi-center Randomized Controlled Trial aimed at evaluating the effectiveness of this system with respect to conventional therapy for sub-acute stroke upper limb rehabilitation. The RETRAINER system consists of a lightweight and non-cumbersome passive arm exoskeleton for weight relief, a current-controlled stimulator with 2 channels of stimulation and 2 channels of EMG recordings. In this work we are presenting the preliminary results of 39 sub-acute stroke patients with a distance from the acute event between two weeks and nine months. The inclusion criteria was: age between 18 and 85 years, Motricity Index (MI) < 80%, muscular activity for arm and shoulder at least 1 Medical Research Council (MRC) with a visible contraction, no joint limitation, pain or spasticity. They were randomized in two group: 1 conventional rehabilitation methods, 2 experimental group using Retrainer System. Each participant performed 9 weeks of treatment 3 times for week. We measured MI, Action Research Arm Test (ARAT) and Motor Activity Log (MAL) at beginning (T0) and at the end of treatment (T1). Results are showed in the next Table 1 . Both groups showed statistical improvement in outcome measures. Experimental group showed a statistical better improvement regarding time and group effect.

Upper Arm Exoskeleton Using Robotic Arm for Physiotherapy

Stroke is a major cause of disability in worldwide and also one of the causes of death after coronary heart disease. Many devices had been designed for hand motor function rehabilitation that a stroke survivor can use for bilateral movement practice. This paper deals with the rehabilitation of upper arm by an Arm exoskeleton. This can be used for physical therapy and to assist the user with routine activities. Ultimately, the user should feel as if they are in control of their arm without too much effort while providing smooth movements depending on the direction that is desired.

ПРИМЕНЕНИЕ ЭКЗОСКЕЛЕТА РУКИ С ФУНКЦИЕЙ «ЗЕРКАЛЬНОГО ДВИЖЕНИЯ» В РЕАБИЛИТАЦИОННЫХ ЦЕЛЯХ

Aim. The aim of this article is to develop the prototype of arm exoskeleton for the treatment of upper limb movement activity after intracerebral hemorrhage or heart attack. Materials and methods. “Movement-mirroring” function was introduced with the help of the manipulating device consisting of the device for wireless data transfer, Arduino controller, exoskeleton servomotors, 3 accelerometers GY-85 and software, which detects angles. Results. We developed the prototype of the rehabilitation device, which was tested by 6 volunteers. Arduino controller allowed us to reduce the time needed for servomotor response up to 400 msec. Conclusion. If only one arm is affected as a result of hemiparesis or hemiplegia, then the rehabilitation therapy can be conducted in accordance with the program stated or by copying the movements of a healthy limb by means of ‘movement-mirroring’ function.

Adjusting the natural stiffness of a pneumatic powered exoskeleton designed as a virtual reality haptic device

This study describes the natural stiffness of a pneumatic powered exoskeleton arm, designed as a haptic device in virtual reality applications. It is important for the haptic device to provide a natural, safe, and comfortable physical mutual human–robot interaction as well as realism for the haptic feedback. To meet these requirements, an exoskeleton possessing an actuation system based on pneumatic artificial muscles and feedforward impedance control is presented. A natural stiffness controller is included to passively adjust the desired stiffness of the exoskeleton. The parameters of the actuation system that determine the natural exoskeleton stiffness are analyzed. A scheme is constructed for joint torque control and end-effector stiffness adjustment under the antagonistic action of the pairs of pneumatic actuators. An optimization-based approach is created for specifying the parameters determining the natural stiffness of the exoskeleton arm. Computer simulations are conducted for a preliminary assess...

The effects of auditory and visual cues on timing synchronicity for robotic rehabilitation.

In this paper, we explore how the integration of auditory and visual cues can help teach the timing of motor skills for the purpose of motor function rehabilitation. We conducted a study using Amazon's Mechanical Turk in which 106 participants played a virtual therapy game requiring wrist movements. To validate that our results would translate to trends that could also be observed during robotic rehabilitation sessions, we recreated this experiment with 11 participants using a robotic wrist rehabilitation system as means to control the therapy game. During interaction with the therapy game, users were asked to learn and reconstruct a tapping sequence as defined by musical notes flashing on the screen. Participants were divided into 2 test groups: (1) control: participants only received visual cues to prompt them on the timing sequence, and (2) experimental: participants received both visual and auditory cues to prompt them on the timing sequence. To evaluate performance, the timing and length of the sequence were measured. Performance was determined by calculating the number of trials needed before the participant was able to master the specific aspect of the timing task. In the virtual experiment, the group that received visual and auditory cues was able to master all aspects of the timing task faster than the visual cue only group with p-values < 0.05. This trend was also verified for participants using the robotic arm exoskeleton in the physical experiment.

Modifying upper-limb inter-joint coordination in healthy subjects by training with a robotic exoskeleton

BackgroundThe possibility to modify the usually pathological patterns of coordination of the upper-limb in stroke survivors remains a central issue and an open question for neurorehabilitation. Despite robot-led physical training could potentially improve the motor recovery of hemiparetic patients, most of the state-of-the-art studies addressing motor control learning, with artificial virtual force fields, only focused on the end-effector kinematic adaptation, by using planar devices. Clearly, an interesting aspect of studying 3D movements with a robotic exoskeleton, is the possibility to investigate the way the human central nervous system deals with the natural upper-limb redundancy for common activities like pointing or tracking tasks.MethodsWe asked twenty healthy participants to perform 3D pointing or tracking tasks under the effect of inter-joint velocity dependant perturbing force fields, applied directly at the joint level by a 4-DOF robotic arm exoskeleton. These fields perturbed the human natural inter-joint coordination but did not constrain directly the end-effector movements and thus subjects capability to perform the tasks. As a consequence, while the participants focused on the achievement of the task, we unexplicitly modified their natural upper-limb coordination strategy. We studied the force fields direct effect on pointing movements towards 8 targets placed in the 3D peripersonal space, and we also considered potential generalizations on 4 distinct other targets. Post-effects were studied after the removal of the force fields (wash-out and follow up). These effects were quantified by a kinematic analysis of the pointing movements at both end-point and joint levels, and by a measure of the final postures. At the same time, we analysed the natural inter-joint coordination through PCA.ResultsDuring the exposition to the perturbative fields, we observed modifications of the subjects movement kinematics at every level (joints, end-effector, and inter-joint coordination). Adaptation was evidenced by a partial decrease of the movement deviations due to the fields, during the repetitions, but it occurred only on 21% of the motions. Nonetheless post-effects were observed in 86% of cases during the wash-out and follow up periods (right after the removal of the perturbation by the fields and after 30 minutes of being detached from the exoskeleton). Important inter-individual differences were observed but with small variability within subjects. In particular, a group of subjects showed an over-shoot with respect to the original unexposed trajectories (in 30% of cases), but the most frequent consequence (in 55% of cases) was the partial persistence of the modified upper-limb coordination, adopted at the time of the perturbation. Temporal and spatial generalizations were also evidenced by the deviation of the movement trajectories, both at the end-effector and at the intermediate joints and the modification of the final pointing postures towards targets which were never exposed to any field.ConclusionsSuch results are the first quantified characterization of the effects of modification of the upper-limb coordination in healthy subjects, by imposing modification through viscous force fields distributed at the joint level, and could pave the way towards opportunities to rehabilitate pathological arm synergies with robots.

Design of a 7-DOF Cable-Driven Arm Exoskeleton (CAREX-7) and a Controller for Dexterous Motion Training or Assistance

The training for both translation and rotation of the hand is desirable for patients with impairments. This paper focuses on the design and control of a 7-degree-of-freedom cable-driven arm exoskeleton (CAREX-7), used for dexterous motion (including translation and rotation) training or assistance of the whole-arm. The CAREX-7 includes an additional wrist module compared with CAREX, and eight cables are routed through the exoskeleton cuffs to drive the whole-arm motion. Based on the “assist-as-needed” paradigm, a novel wrench-field controller was designed to regulate a needed wrench (force and torque) on the hand for assisting its dexterous manipulation. Healthy subjects participated in path-tracking experiments while wearing CAREX-7. The experimental results show that the CAREX-7 with the new wrench-field controller can help the subjects to follow the path more closely, and this demonstrates the effectiveness of the device. The current design of CAREX-7 is unique and offers significant improvements and new functionality over the existing CAREX. The novel features are the following: 1) CAREX-7 is an exoskeleton for the full human arm, including shoulder, elbow, and the wrist, with new design issues; and 2) controller of CAREX-7 builds on a screw-theoretic approach and assists both translation and rotation of the hand, allowing for dexterous hand reorientation, which is required in everyday tasks.

Closed-Loop Task Difficulty Adaptation during Virtual Reality Reach-to-Grasp Training Assisted with an Exoskeleton for Stroke Rehabilitation.

Stroke patients with severe motor deficits of the upper extremity may practice rehabilitation exercises with the assistance of a multi-joint exoskeleton. Although this technology enables intensive task-oriented training, it may also lead to slacking when the assistance is too supportive. Preserving the engagement of the patients while providing “assistance-as-needed” during the exercises, therefore remains an ongoing challenge. We applied a commercially available seven degree-of-freedom arm exoskeleton to provide passive gravity compensation during task-oriented training in a virtual environment. During this 4-week pilot study, five severely affected chronic stroke patients performed reach-to-grasp exercises resembling activities of daily living. The subjects received virtual reality feedback from their three-dimensional movements. The level of difficulty for the exercise was adjusted by a performance-dependent real-time adaptation algorithm. The goal of this algorithm was the automated improvement of the range of motion. In the course of 20 training and feedback sessions, this unsupervised adaptive training concept led to a progressive increase of the virtual training space (p < 0.001) in accordance with the subjects' abilities. This learning curve was paralleled by a concurrent improvement of real world kinematic parameters, i.e., range of motion (p = 0.008), accuracy of movement (p = 0.01), and movement velocity (p < 0.001). Notably, these kinematic gains were paralleled by motor improvements such as increased elbow movement (p = 0.001), grip force (p < 0.001), and upper extremity Fugl-Meyer-Assessment score from 14.3 ± 5 to 16.9 ± 6.1 (p = 0.026). Combining gravity-compensating assistance with adaptive closed-loop feedback in virtual reality provides customized rehabilitation environments for severely affected stroke patients. This approach may facilitate motor learning by progressively challenging the subject in accordance with the individual capacity for functional restoration. It might be necessary to apply concurrent restorative interventions to translate these improvements into relevant functional gains of severely motor impaired patients in activities of daily living.