Feedback Control of an Exoskeleton for Paraplegics: Toward Robustly Stable Hands-free Dynamic Walking

This manuscript presents control of a high-DOF fully actuated lower-limb exoskeleton for paraplegic individuals. The key novelty is the ability for the user to walk without the use of crutches or other external means of stabilization. We harness the power of modern optimization techniques and supervised machine learning to develop a smooth feedback control policy that provides robust velocity regulation and perturbation rejection. Preliminary evaluation of the stability and robustness of the proposed approach is demonstrated through the Gazebo simulation environment. In addition, preliminary experimental results with (complete) paraplegic individuals are included for the previous version of the controller.Comment: Submitted to IEEE Control System Magazine. This version addresses reviewers' concerns about the robustness of the algorithm and the motivation for using such exoskeleton

A Review of Lower Limb Exoskeletons

In general, exoskeletons are defined as wearable robotic mechanisms for providing mobility. In the last six decades, many research work have been achieved to enhance the performance of exoskeletons thus developing them to nearly commercialized products. In this paper, a review is made for the lower limb exoskeleton concerning history, classification, selection and development, also a discussion for the most important aspects of comparison between different designs is presented. Further, some concluding remarks are withdrawn which could be useful for future work. Keywords: Exoskeletons, Lower extremity exoskeleton, Wearable robot

Role of Gait Training in Recovery of Standing and Walking in Subjects with Spinal Cord Injury

Gait training has an important role in rehabilitation of standing and walking in spinal cord injury (SCI) patients. There were different types of gait training in these subjects. Both the body weight support treadmill training and robotic-assisted and robotic exoskeleton are effective and secure methods for gait training and improving the energy demand and metabolic cost in SCI patients in different level of injury. The powered exoskeletons can provide patients with SCI the ability to walk with the lowest energy consumption. The powered exoskeleton’s energy consumption and speed of walking depend on the training duration. Based on different types of gait training methods, training time, and other affected parameters, the aim of this chapter was to evaluate the role of gait training in recovery of standing and walking in SCI patients

Comfort-Centered Design of a Lightweight and Backdrivable Knee Exoskeleton

This paper presents design principles for comfort-centered wearable robots and their application in a lightweight and backdrivable knee exoskeleton. The mitigation of discomfort is treated as mechanical design and control issues and three solutions are proposed in this paper: 1) a new wearable structure optimizes the strap attachment configuration and suit layout to ameliorate excessive shear forces of conventional wearable structure design; 2) rolling knee joint and double-hinge mechanisms reduce the misalignment in the sagittal and frontal plane, without increasing the mechanical complexity and inertia, respectively; 3) a low impedance mechanical transmission reduces the reflected inertia and damping of the actuator to human, thus the exoskeleton is highly-backdrivable. Kinematic simulations demonstrate that misalignment between the robot joint and knee joint can be reduced by 74% at maximum knee flexion. In experiments, the exoskeleton in the unpowered mode exhibits 1.03 Nm root mean square (RMS) low resistive torque. The torque control experiments demonstrate 0.31 Nm RMS torque tracking error in three human subjects.Comment: 8 pages, 16figures, Journa

Feasibility and efficacy of incorporating an exoskeleton in gait training during subacute stroke rehabilitation

Introduction: Hemiparesis is the most common acute manifestation of stroke and often has a strong negative impact on walking ability leaving one third of patients dependent in walking activities outside one’s home. Improved methods for training of gait during stroke rehabilitation could tackle the challenge of achieving independent walking and promote better outcomes. Several studies have explored the value of introducing electromechanical gait machines in stroke rehabilitation to enhance gait training. One example is the exoskeleton Hybrid Assistive Limb (HAL). The HAL system has been found feasible to use during rehabilitation in the chronic stage after stroke, however knowledge of the feasibility in the subacute stage after stroke and its efficacy compared to evidence-based conventional gait training is still limited. Aim: The overall aim of this thesis was to evaluate the safety and feasibility of HAL for gait training in the subacute stage after stroke and the effect of HAL training on functioning, disability and health compared to conventional gait training, as part of an inpatient rehabilitation program in patients with severe limitations in walking in the subacute stage after stroke. Methods: This thesis contains two studies where one is a safety and feasibility study (Study I) and one is a prospective, randomized, open labeled, blinded evaluation study (Study II). In Study I, eight patients performed HAL training 5 days/week. The number of training sessions were adjusted individually and varied from 6 to 31 (median 16). Safety and feasibility aspects of the training were evaluated as well as clinical outcomes on functioning and disability (e.g. independence in walking, walking speed, balance, movement functions and activities of daily living), assessed before and after the intervention period. In Study II, 32 patients were randomized to either conventional training only or HAL training in addition to the conventional training, 4 days per week for 4 weeks. Within and between- group differences in independence in walking, walking speed/endurance, balance, movement functions and activities of daily living were investigated before and after the intervention period, as well as 6 months post stroke. In addition, gait pattern functions were evaluated after the intervention in a three-dimensional gait laboratory. At 6 months post stroke self- perceived aspects on functioning disability and health were assessed and subsequently correlated to the clinical assessments. Results: In Study I HAL was found to be safe and feasible for gait training after stroke in patients with hemiparesis, unable to walk independently, undergoing an inpatient rehabilitation program. All patients improved in walking independence and speed, movement function, and activities of daily living during the intervention period. In addition, it was found that patients walked long distances during the HAL sessions, suggesting that HAL training may be an effective method to enhance gait training during rehabilitation of patients in the subacute stage after stroke. In Study II substantial but equal improvements in the clinically evaluated outcomes in the two intervention groups were found. At six months post stroke, two thirds of patients were independent in walking, and a younger age but not intervention group served as the best predictor. Gait patterns were similarly impaired in both groups and in line with previous reports on gait patterns post stroke. Further, self-perceived ratings on functioning, disability and health were explained by the ability to perform self-care activities and not by intervention group. Conclusion: To incorporate gait training with HAL is safe and feasible during inpatient rehabilitation in the subacute stage after stroke and may be a way to increase the dose (i.e. number of steps) in gait training in the subacute stage after stroke. Among these included younger patients with hemiparesis and severe limitations in walking in the subacute stage after stroke, substantial improvements in body function and activity as well as equally impaired gait patterns were observed both after incorporated HAL training and after conventional gait training only, but without between-group differences. In future studies, potential beneficial effects on cardiovascular, respiratory, and metabolic functions should be addressed. Further, as the stroke population is heterogeneous, potential subgroups of patients who may benefit the most from electromechanically-assisted gait training should be identified

The Use of Lower Extremity Functional Electrical Stimulation in Spinal Cord Injured Patients

Spinal cord injury (SCI) is a devastating, life-altering injury that presents a variety of rehabilitative and long-term medical management challenges. Not only must the inability to ambulate, which is generally of primary concern to the patient, be addressed, but also the inherent degenerative and deconditioning effects of SCI which may ultimately lead to various secondary complications. Recently, functional electrical stimulation (FES) has been the subject of a variety of research concerning the rehabilitation of individuals with SCI. FES is a means of activating alpha motor neurons to stimulate muscular contraction and elicit a therapeutic or functional effect. The purpose of this paper is to examine and review current uses of FES in the spinal cord injured individual to restore functional movement of the lower extremities. Specifically, it will focus on muscle conditioning, cardiovascular conditioning, and control of standing and ambulation with an explanation of the physiologic effect of each of these activities. The role of FES in combating and preventing secondary complications of SCI will also be reviewed. This paper will involve an extensive literature review of the topics. The results of this paper will aid physical therapists in the clinical management of SCI through the use of FES