Design and Evaluation of a Semi-Active Single-Leg Exoskeleton for Walking Assistance of Children with Muscular Weakness

Lower-limb exoskeletons have potential to increase endurance, reduce incidence of injury, aid rehabilitation and prolong independence. Progress in exoskeleton research is slowed by the complex nature of exoskeleton design and by the complexity of the humans they are supposed to assist. Developing highly versatile tools to address these issues will accelerate research and bring exoskeletons closer to becoming life changing products. This thesis details an approach to exoskeleton development that leverages both universal exoskeleton emulators and human-in-the-loop optimization to enable accurate comparisonsof qualitatively different exoskeleton assistance strategies. Instead of building new or adjusting old hardware to test a given exoskeleton design, we developed highly capable,lightweight, tethered exoskeletons that were used to emulate the behavior of a wide variety of possible exoskeleton designs. The development of these exoskeleton emulators revealed guiding principles of lower-limb exoskeleton design that will aid in the creationof future exoskeletons. Experimental comparisons of exoskeleton control architectures for walking and running were performed to determine the most promising strategies to pursue. Passive, spring-like assistance was compared to powered assistance for running. Threequalitatively different assistance strategies were explored for assisting walking. Included among the walking assistance strategies was a first look at an EMG-based muscle-tendoncontroller. This controller applied a muscle-tendon model to measured EMG activity to produce exoskeleton assistance in a manner similar to human muscle. In both the walking and running experiments, human-in-the-loop optimization was performed to provide customization of exoskeleton settings to fit the needs of individual subjects. This enabled a more accurate comparison of candidate assistance strategies. We expect our findings to influencethe design of portable, untethered ankle exoskeletons and to proliferate the use of emulator systems in combination with human-in-the-loop optimization to perform side-by-sidecomparisons of assistance strategies.

In the development of assistive lower-limb exoskeletons, both exoskeleton design, and gait control are critical for their successful applications. This paper introduces an assistive lower-limb exoskeleton (ALEXO) for active walking assistance. The development of the ALEXO including mechanical design, sensors and gait control is described. The exoskeleton adopts a hierarchical control. A 2-link model is built for dynamic analysis and lower-level control purposes. A trajectory tracking control method based on the computed torque control is proposed, in which physical interaction between the exoskeleton and the user is included. Simulations were conducted for different levels of interaction forces to verify the feasibility of the gait control. Moreover, walking trials of a healthy subject were performed, with muscle activities measured through EMG systems. Both simulation and system test results demonstrated the effectiveness of the developed exoskeleton with the proposed control method for walking assistance.

Design, control and evaluation of a lower limb wearable robotic exoskeleton for power assistance are presented in the paper. The proposed four degree-of-freedom robotic exoskeleton, an active flexion/extension and a passive abduction/adduction rotation at each hip joint, is characterized with complying with the swinging motion of lower limbs as close as possible. To perform power assistance on walking, the linear extended state observer (LESO) based controllers were designed for the walking assistance. Finally, the experiments were conducted to validate the prototype of lower limb robotic exoskeleton. The associated evaluations for the walking assistance were also investigated using the motion captured system and EMG signal.

This paper illustrates the design and testing of a lower limb exoskeleton for walking assistance. First, the biomechanics of the human knee and ankle joints during walking and the strategy of energy recycling and releasing are introduced. Next, the hardware design of the exoskeleton is described. The exoskeleton is primarily composed of a waist module, a knee module, and an ankle module. Two clutch mechanisms are designed for one-way motion transmission, and an energy storage spring is designed to store the energy recycled from the human knee motion. Additionally, the modeling of the human-exoskeleton system is presented. Finally, experiments are conducted to verify the effectiveness of the developed exoskeleton. The experimental results demonstrate that the exoskeleton has the potential to recycle the negative work from the wearer’s knee flexion during the late stance phase and knee extension during the swing phase to assist the wearer’s ankle plantarflexion during the stance phase. During a gait cycle, reductions of 11.6% and 15.6% of the average muscle activities of the gastrocnemius and soleus are observed, respectively. In addition, the peak gastrocnemius and soleus activities during the push-off stage are reduced by 16.9% and 42.6%, respectively.

This paper presents an assistive lower-limb exoskeleton (ALEXO) for active walking assistance. The mechatronics design covering mechanical design, sensors selection and motor controllers are introduced. A 2-link model is built for dynamic analysis control purposes, upon which a trajectory tracking control method based on an improved computed torque control is proposed. This control method was tested with sensor data acquired from walking trials of a healthy subject, which validated the design and gait control of this exoskeleton.

This paper presents a study on a compliant cable-driven exoskeleton for hip assistance in lifting tasks that is aimed at preventing low-back pain and injuries in the vocational setting. In the proposed concept, we used twisted string actuator (TSA) to design a light-weight and powerful exoskeleton that benefits from inherent TSA advantages. We have noted that nonlinear nature of twisted strings' transmission ratio (decreasing with twisting) closely matched typical torque-speed requirements for hip assistance during lifting tasks and tried to use this fact in the exoskeleton design and motor selection. Hip-joint torque and speed required to lift a 10-kg load from stoop to stand were calculated, which gave us a baseline that we used to design and manufacture a practical exoskeleton prototype. Preliminary experimental trials demonstrated that the proposed device was capable of generating required torque and speed at the hip joint while weighing under 6 kg, including battery.

In recent years, soft robotic rehabilitation and assistive exoskeletons have gained significant attention due to their potential to enhance human mobility and improve rehabilitation outcomes.This paper focuses on the design of a Cable-Driven Soft Elbow Exoskeleton, specifically developed to provide a lightweight, comfortable, and user-friendly solution for rehabilitation and movement assistance.The exoskeleton integrates a Myoelectric Model Reference Adaptive Controller, enabling two operational modes: passive mode, where the system assists movement without requiring user effort, and myoelectric active mode, which allows voluntary user control with adaptive torque assistance.The proposed design prioritizes ergonomics, ease of use, and adaptability to different rehabilitation needs, making it a promising tool for enhancing physical therapy interventions.

This paper deals with the mechanical design of a novel assistive exoskeleton for the paraplegic and the elderly. In order to reduce the inconvenience that traditional devices have in long distance travel, this paper developed a deformable exoskeleton which merges the exoskeleton and the wheelchair. What have been taken into consideration include the characteristics of human joints, DOF configuration, actuator characteristics and human-machine interaction. Then according to these factors, this paper introduced the deformation principle based on the four-bar linkage and designed the hip and knee joint structures. Finally, this paper analyzed the stability of the deformation process with CoG judgement, proved the feasibility and introduced an adjustment method to improve the stability margin to avoid the risk of turnover when facing slopes.

In this study, we describe the mechanical design and control scheme of a quasi-passive knee exoskeleton intended to investigate the biomechanical behavior of the knee joint during interaction with externally applied impedances. As the human knee behaves much like a linear spring during the stance phase of normal walking gait, the exoskeleton implements a spring across the knee in the weight acceptance (WA) phase of the gait while allowing free motion throughout the rest of the gait cycle, accomplished via an electromechanical clutch. The stiffness of the device is able to be varied by swapping springs, and the timing of engagement/disengagement changed to accommodate different loading profiles. After describing the design and control, we validate the mechanical performance and reliability of the exoskeleton through cyclic testing on a mechanical knee simulator. We then describe a preliminary experiment on three healthy adults to evaluate the functionality of the device on both left and right legs. The kinetic and kinematic analyses of these subjects show that the exoskeleton assistance can partially/fully replace the function of the knee joint and obtain nearly invariant moment and angle profiles for the hip and ankle joints, and the overall knee joint and exoskeleton complex under the applied moments of the exoskeleton versus the control condition, implying that the subjects undergo a considerable amount of motor adaptation in their lower extremities to the exoskeletal impedances, and encouraging more in-depth future experiments with the device.

Assistive Exoskeleton is a type of ergonomic product that is based on exoskeleton support and is a chair. Standing for five hours or more each day, according to a small study, increases the risk of considerable and prolonged lower-limb muscular fatigue. Long-term back pain and musculoskeletal problems may be increased as a result of this. Meanwhile, the researchers discovered that persons who primarily stand at work are several percent more likely than "predominantly sitting populations" to suffer heart disease. Because of its big size, high weight (5 to 7 kg), and hard frame, the traditional chair is inconvenient to transport to different working locations. As a result, they are unsuited for workplaces with limited space. Because lightweight members are used, the flexible wearable chair may have a gross weight of 3 kg. It has to be constructed in such a way that workers may be comfortable while performing their activities and can adjust their sitting posture to any angle between 90 and 160 degrees. This exoskeleton can be used as an extra pair of legs to allow a person to sit without using a chair or to adopt a more comfortable position for certain occupations. Workers can walk around normally, but they must adjust and secure the supporting structure in the proper position if they want to sit or lean. The weight is then balanced on the floor by their movable frames. It's designed for factory workers who must stand for extended periods of time in work and occasionally bend into unusual positions to build a product. Spatial management is a critical aspect in every industry. By optimizing the utilization of an Assistive Exoskeleton, superfluous chairs and resting areas can be avoided.

Actuation transparency and safety are important requirements in the design and control of assistive exoskeletons for individuals who suffer lower limb deficits but still maintain a certain level of voluntary motor control. In recent years, series elastic actuator (SEA) has been regarded as a promising solution for transparent actuation and safe human–robot interaction, thus SEAs are widely developed and applied in assistive exoskeletons. However, existing SEAs designed for assistive exoskeletons still lack both actuation transparency and safety because of high stiffness of the elastic element and the high mechanical impedance of the actuators. To address this problem, a novel nonlinear SEA (nSEA) is presented in this article. The optimized nonlinear series elastic element coupled with a quasi-direct drive motor creates the nSEA with low mechanical impedance, high backdrivability, and less acoustic noise. Besides, a new torque control, based on cascade PI control, is proposed for the nSEA to control the interaction torque with high accuracy and robustness. Finally, an experimental evaluation with human subjects is performed to validate the advantages of the nSEA-driven hip exoskeleton in the realization of actuation transparency and safety. The root-mean-square interaction torque in zero-impedance mode is as low as 0.051 N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\cdot$</tex-math></inline-formula> m during walking conditions, leading to a negligible negative influence on the hip joint's range of motion, walking speed, and energy expenditure when wearing the hip exoskeleton.

Series elastic actuators (SEAs) are commonly used in ankle exoskeletons for friendly human-robot interaction and high power efficiency. However, most ankle exoskeletons face a common performance limitation due to the use of fixed stiffness series springs. In this paper, we present an adaptive ankle exoskeleton for walking assistance. A novel compact variable stiffness SEA with a non-linear spring, which is able to passively change the spring stiffness as a function of output load, is developed to overcome the limitation of the conventional SEAs. The predefined nonlinear elasticity of the proposed passively variable stiffness SEA (pVS-SEA) is achieved with a cam mechanism and leaf springs, which result in a compact design. Furthermore, a variable transmission mechanism is adopted to modulate the physical exoskeleton stiffness as a function of ankle joint angle. The exoskeleton mechanism is optimized based on the human gait data by employing a genetic algorithm. The results show that the presented ankle exoskeleton is adaptable under different walking conditions, and the energy efficiency of the system is improved compared with the conventional ones.

Exoskeletons are human-robot interfaces that have enormous potential to assist people with everyday tasks. To improve the design of exoskeletons for use in clinical populations, it is important to further our understanding of how exoskeleton design and control parameters lead to sub-optimal effectiveness. Here we simulated the effect of three factors, gait variability, wearer-exoskeleton delays, and exoskeleton inertia, have on the predicted energy assistance provided by an exoskeleton with a finite-state controller trained on a set of stroke survivors' free walking gait data. Results indicate that larger errors between the wearer's desired ankle trajectory and the exo's estimated ankle trajectory result in statistically large reductions in the actual assistance provided. Specifically lags on the order of even 10 ms can illustrate statistically sub-optimal performance. Likewise subjects that exhibit large gait variability will have a statistical reduction in actual assistance. However, reasonably low exoskeleton inertias are not significant as a factor in terms of sensitivity to wearer assistance. Therefore, to improve cooperative control algorithms for exoskeletons and achieve true assistance based on wearer induced motion, this work implies that designers should prioritize minimizing delays and wearers should train to reduce variability in order to maximize energy savings.

Exoskeletons can augment the performance of unimpaired users and restore movement in individuals with gait impairments. Knowledge of how users interact with wearable devices and of the physiology of locomotion have informed the design of rigid and soft exoskeletons that can specifically target a single joint or a single activity. In this Review, we highlight the main advances of the past two decades in exoskeleton technology and in the development of lower-extremity exoskeletons for locomotor assistance, discuss research needs for such wearable robots and the clinical requirements for exoskeleton-assisted gait rehabilitation, and outline the main clinical challenges and opportunities for exoskeleton technology.

Most of the upper limb exoskeletons proposed in the literature are designed for rehabilitation, however, there are few developments for activities assistance of daily living. This paper presents a wearable upper limb exoskeleton for activities assistance of daily living with the feature of mobility. It provides five degrees-of-freedom (DOF) for each arm, where 3 DOF and 2 DOF are given to the shoulder and elbow, respectively. And it allows the wearer to keep freedom and mobility as usual after wearing the device. To conquer the strength-to-weight limitations of exoskeleton mobility, we introduced gravity balance method to reduce energy consumption and proposed a novel cable-driven joint mechanism to reduce its total weight to 4.2 kg. In order to verify the plausibility of joints design and its performance on motion assistance, joints tracking test and motion assistance test were carried out, respectively. Their results support that the proposed exoskeleton is feasible and efficacious.