Leg Exoskeleton Research Articles

"DESIGN AND OPTIMIZATION OF WEARABLE ACTIVE WAIST AND LEG EXOSKELETON STRUCTURE FOR MINING"

"DESIGN AND OPTIMIZATION OF WEARABLE ACTIVE WAIST AND LEG EXOSKELETON STRUCTURE FOR MINING"

Multicriteria Optimization of Lower Limb Exoskeleton Mechanism

Typical leg exoskeletons employ open-loop kinematic chains with motors placed directly on movable joints; while this design offers flexibility, it leads to increased costs and heightened control complexity due to the high number of degrees of freedom. The use of heavy servo-motors to handle torque in active joints results in complex and bulky designs, as highlighted in the existing literature. In this analytical study, we introduced a novel synthesis method with analytical solutions provided for synthesizing the lower-limb exoskeleton. Furthermore, we proposed a mathematical model of multicriteria optimization; as a result, we obtained several lower-limb exoskeleton mechanisms comprising only six links, well-suited to the human anatomical structure, exhibit superior trajectory accuracy, efficient force transmission, satisfactory step height, and having internal transfer segment of the foot.

A Novel Exoskeleton Design and Numerical Characterization for Human Gait Assistance

This paper addressed attention to the design of a new lower limb exoskeleton that can be used for human gait assistance as based on kinematic considerations. The designed leg exoskeleton had on its own structure a combination of three mechanism types, namely a Chebyshev mechanism, a pantograph, and a Stephenson six-bar mechanism. The design core focused on inserting the Stephenson six-bar bar mechanism in order to obtain an imposed motion at the ankle joint level. Numerical simulations of the designed lower limb exoskeleton have been developed and the obtained results demonstrate the engineering feasibility of the proposed prototype, with a characterization of satisfactory operation performance.

Trophic discrimination factors and stable isotope variability in a captive feeding trial of the southern rock lobster Jasus edwardsii () (Decapoda: Palinuridae) in Tasmania, Australia

Abstract Trophic discrimination or fractionation factors (TDFs), such as ∆15N and ∆13C, are used in stable isotope mixing models to account for differences between source tissues (diet/prey) and consumer tissues (predator). We aimed firstly to obtain TDF values for a spiny lobster, the southern rock lobster Jasus edwardsii (Hutton, 1875), to better understand lobster diet in the wild and secondly to investigate variability in isotope signature within tissues of individuals and across a temporal scale to test if non-lethal sampling can be used in an ecological context. We conducted an 18-mo captive feeding trial with juvenile lobsters using three diet treatments and analysed dorsal and leg muscle, along with dorsal and leg exoskeleton for δ13C and δ15N values. Average TDFs for the three diet treatments were 3.86 ± 0.98‰ (∆13C) and 5.06 ± 0.65‰ (∆15N) for leg muscle, and 4.45 ± 1.04‰ (∆13C) and 4.36 ± 0.6‰ (∆15N) for dorsal muscle. When tested against wild lobsters and prey, these TDFs outperformed multi-taxa TDFs found in the literature. Isotope values from lobster leg muscle were not identical to associated dorsal muscle but the two were highly correlated, indicating that non-lethal sampling is acceptable. Values for exoskeleton isotope were significantly different from muscle, likely due to the exoskeleton not being in a constant state of growth and replacement, unlike the muscle tissue, which constantly incorporates new material. We conclude that our experimentally derived TDFs are suitable for mixing model analysis for J. edwardsii and when tested on a wild sample of lobsters they outperformed other TDFs reported in the literature. We show that non-lethal sampling using leg muscle is an appropriate sampling method, since this tissue is highly correlated to the commonly used dorsal muscle. This option for non-lethal sampling enhances the potential to widely sample wild populations or sample during industrial processing without the need to sacrifice whole animals.

Spatial Repetitive Impedance Learning Control for Robot-Assisted Rehabilitation

In robot-assisted rehabilitation and leg exoskeletons, humans and robots are required to collaboratively complete repetitive tasks with fixed periodic paths. In such applications, impedance learning control can provide variable impedance regulation for improving the performance of physical interactions; however, designing such control is highly challenging owing to the difficulty in modeling human time-varying dynamics. By exploiting the spatial periodicity characteristics of the desired trajectory and human impedance, we propose a novel spatial repetitive impedance learning control strategy to enhance interaction performance. First, a defined spatial operator serves as the mathematics foundation for constructing the robot dynamics in the spatial domain. Then, a spatial impedance learning controller is designed. In this article, time-varying impedance profiles are estimated using spatial full-saturation iterative learning laws, while robotic parameter uncertainties are estimated using the differential adaptation law with projection modification. We validate the uniform convergence of the tracking error through a Lyapunov-like analysis and demonstrate the control effectiveness using an illustrative example. Compared with related results on temporal repetitive learning control, the proposed control approach can enable human–robot system to complete a repetitive task with unspecified speeds according to the users' strengths and motion capacity.

A mechatronic leg replica to benchmark human–exoskeleton physical interactions

Evaluating human–exoskeleton interaction typically requires experiments with human subjects, which raises safety issues and entails time-consuming testing procedures. This paper presents a mechatronic replica of a human leg, which was designed to quantify physical interaction dynamics between exoskeletons and human limbs without the need for human testing. In the first part of this work, we present the mechanical, electronic, sensory system and software solutions integrated in our leg replica prototype. In the second part, we used the leg replica to test its interaction with two types of commercially available wearable devices, i.e. an active full leg exoskeleton and a passive knee orthosis. We ran basic test examples to demonstrate the functioning and benchmarking potential of the leg replica to assess the effects of joint misalignments on force transmission. The integrated force sensors embedded in the leg replica detected higher interaction forces in the misaligned scenario in comparison to the aligned one, in both active and passive modalities. The small standard deviation of force measurements across cycles demonstrates the potential of the leg replica as a standard test method for reproducible studies of human-exoskeleton physical interaction.

Adaptive load feedback robustly signals force dynamics in robotic model of Carausius morosus stepping.

Animals utilize a number of neuronal systems to produce locomotion. One type of sensory organ that contributes in insects is the campaniform sensillum (CS) that measures the load on their legs. Groups of the receptors are found on high stress regions of the leg exoskeleton and they have significant effects in adapting walking behavior. Recording from these sensors in freely moving animals is limited by technical constraints. To better understand the load feedback signaled by CS to the nervous system, we have constructed a dynamically scaled robotic model of the Carausius morosus stick insect middle leg. The leg steps on a treadmill and supports weight during stance to simulate body weight. Strain gauges were mounted in the same positions and orientations as four key CS groups (Groups 3, 4, 6B, and 6A). Continuous data from the strain gauges were processed through a previously published dynamic computational model of CS discharge. Our experiments suggest that under different stepping conditions (e.g., changing "body" weight, phasic load stimuli, slipping foot), the CS sensory discharge robustly signals increases in force, such as at the beginning of stance, and decreases in force, such as at the end of stance or when the foot slips. Such signals would be crucial for an insect or robot to maintain intra- and inter-leg coordination while walking over extreme terrain.

Design Approaches of an Exoskeleton for Human Neuromotor Rehabilitation

This paper addresses a design for an exoskeleton used for human locomotion purposes in cases of people with neuromotor disorders. The reason for starting this research was given by the development of some intelligent systems for walking recovery involved in a new therapy called stationary walking therapy. This therapy type will be used in this research case, through a robotic system specially designed for functional walking recovery. Thus, the designed robotic system structure will have a patient lifting/positioning mechanism, a special exoskeleton equipped with sensors and actuators, a treadmill for walking, and a command and control unit. The exoskeleton’s lower limbs will have six orthotic devices. Thus, the exoskeleton’s lower limbs’ motions and orthoses angle variations will be generated by healthy human subjects on the treadmill with the possibility of memorizing these specific motions for obtaining one complete gait cycle. After this, the memorized motions will be performed to a patient with neuromotor disorders for walking recovery programs. The design core is focused on two planar-parallel mechanisms implemented at the knee and ankle joints of each leg’s exoskeleton. Thus, numerical simulations for the design process were carried out to validate the engineering feasibility of the proposed leg exoskeleton.

Dynamic Parameter Identification of a Human-Exoskeleton System With the Motor Torque Data

The objective of this paper is to identify dynamic parameters of the human-exoskeleton system (HES) with the motor torque data considering modeling the passive elastic joint torque of the user. Based on a lower limb exoskeleton prototype we recently developed, the dynamics of the joint actuators and two degrees of freedom link-based swing leg are firstly modeled. The passive elasticity of the human joint is modeled by double-exponential equations. Systematic experiments are then conducted, during which the motor current is measured to compute the motor torque for identification. Finally, the dynamic parameters of the joint actuators, the exoskeleton leg and the human-exoskeleton leg are successively identified. The identification is implemented through the off-line inverse dynamic model simulation with the measured motor torque data. A consistent tendency is found between the simulated motor torque after identification and the measured one. This demonstrates the validity of the identification method proposed. This paper provides a systemic method of identifying the HES with the motor torque data and enriches the experimental proof that the double-exponential model is feasible to describe the passive elastic joint torque.

Assessing effects of exoskeleton misalignment on knee joint load during swing using an instrumented leg simulator

BackgroundExoskeletons are working in parallel to the human body and can support human movement by exerting forces through cuffs or straps. They are prone to misalignments caused by simplified joint mechanics and incorrect fit or positioning. Those misalignments are a common safety concern as they can cause undesired interaction forces. However, the exact mechanisms and effects of misalignments on the joint load are not yet known. The aim of this study was therefore to investigate the influence of different directions and magnitudes of exoskeleton misalignment on the internal knee joint forces and torques of an artificial leg.MethodsAn instrumented leg simulator was used to quantify the changes in knee joint load during the swing phase caused by misalignments of a passive knee brace being manually flexed. This was achieved by an experimenter pulling on a rope attached to the distal end of the knee brace to create a flexion torque. The extension was not actuated but achieved through the weight of the instrumented leg simulator. The investigated types of misalignments are a rotation of the brace around the vertical axis and a translation in anteroposterior as well as proximal/distal direction.ResultsThe amount of misalignment had a significant effect on several directions of knee joint load in the instrumented leg simulator. In general, load on the knee joint increased with increasing misalignment. Specifically, stronger rotational misalignment led to higher forces in mediolateral direction in the knee joint as well as higher ab-/adduction, flexion and internal/external rotation torques. Stronger anteroposterior translational misalignment led to higher mediolateral knee forces as well as higher abduction and flexion/extension torques. Stronger proximal/distal translational misalignment led to higher posterior and tension/compression forces.ConclusionsMisalignments of a lower leg exoskeleton can increase internal knee forces and torques during swing to a multiple of those experienced in a well-aligned situation. Despite only taking swing into account, this is supporting the need for carefully considering hazards associated with not only translational but also rotational misalignments during wearable robot development and use. Also, this warrants investigation of misalignment effects in stance, as a target of many exoskeleton applications.

Simulation of a Walking Robot-Exoskeleton Movement on a Movable Base

The paper studies the problem of movement of a two-legged walking machine on a movable base. This task is relevant for design rehabilitation and mechanotherapy complexes for people with impaired functions of the musculoskeletal system. Presents a mathematical model that allows obtaining the kinematic and dynamic parameters of the movement of the executive units of the device under study. The paper presents a method for planning the trajectory of exoskeleton links, its algorithmic and software implementation. The paper proposes the structure of the automatic link position control system, which ensures the movement of the executive links along a given trajectory. A mathematical apparatus is proposed for studying the dynamics of the controlled movement of the links of the human-machine system of the exoskeleton. The article presents the results of numerical experiments on the movement of the low-limb exoskeleton leg in the one step mode and analyzes them.

Bio-Inspired Knee Joint: Trends in the Hardware Systems Development.

The knee joint is a complex structure that plays a significant role in the human lower limb for locomotion activities in daily living. However, we are still not quite there yet where we can replicate the functions of the knee bones and the attached ligaments to a significant degree of success. This paper presents the current trend in the development of knee joints based on bio-inspiration concepts and modern bio-inspired knee joints in the research field of prostheses, power-assist suits and mobile robots. The paper also reviews the existing literature to describe major turning points during the development of hardware and control systems associated with bio-inspired knee joints. The anatomy and biomechanics of the knee joint are initially presented. Then the latest bio-inspired knee joints developed within the last 10 years are briefly reviewed based on bone structure, muscle and ligament structure and control strategies. A leg exoskeleton is then introduced for enhancing the functionality of the human lower limb that lacks muscle power. The design consideration, novelty of the design and the working principle of the proposed knee joint are summarized. Furthermore, the simulation results and experimental results are also presented and analyzed. Finally, the paper concludes with design difficulties, design considerations and future directions on bio-inspired knee joint design. The aim of this paper is to be a starting point for researchers keen on understanding the developments throughout the years in the field of bio-inspired knee joints.

Efficiency of Leg Exoskeleton Use in Rehabilitation of Cerebral Stroke Patients

Abstract The study aimed to evaluate the effectiveness of functional and motor activity restoration, including the walking function, in patients after an ischemic stroke using the ExoAtlet lower limb exoskeleton. Patients and methods. A clinical study was carried out on 42 patients who had undergone a cerebral infarction in the mid cerebral artery system with a post-stroke paresis of the leg, and who had undergone a rehabilitation course in a round-theclock hospital during the early recovery period. Patients were randomized into two equal groups comparable in terms of the stroke severity: the patients in group 1 were receiving a standard rehabilitation program (control group), the patients in group 2 were additionally receiving a course of gait rehabilitation using the ExoAtlet exoskeleton - 10 sessions, 5 sessions per week for 14 days. Results. The study demonstrated the effectiveness of the ExoAtlet exoskeleton used in the rehabilitation of stroke patients over the standard course of rehabilitation. The advantages include a decrease in the hemiparesis degree, an increase in the muscle strength of the paretic limb, an improvement in balance, an improvement and acceleration of the walking process. The obtained results of the instrumental study confirmed the benefits of physical training on the Exoskeleton, which was demonstrated through an increase in stability and balance, as well as through a decrease in the energy consumption index for maintaining the stable verticalization. Conclusion. The usage of the ExoAtlet exoskeleton increases the effectiveness of rehabilitation measures and improves motor and functional activities of patients who have suffered a cerebral stroke.

Precision force control of an underactuated stance leg exoskeleton for human performance augmentation

Lower limb exoskeleton which augments the human performance is a wearable human–machine integrated system used to assist people carrying heavy loads. Recently, underactuated lower limb exoskeleton systems with some passive joints become more and more attractive due to the advantages of smaller weight, lower system energy consumption and lower cost. However, because of the less of control inputs, the existed control methods of fully actuated exoskeletons cannot be extended to underactuated systems, which makes the robust controller design of underactuated lower limb exoskeletons becomes more challenged. This article focuses on the high-performance human–machine interaction force control design of underactuated lower limb exoskeletons with passive ankle joint. In order to solve the reduction of control inputs, the holonomic constraint from the wearer is considered, which help transform the dynamics of 3-degree-of-freedom underactuated exoskeleton in joint space into a 2-degree-of-freedom fully actuated system in Cartesian space. A two-level interaction force controller using adaptive robust control algorithm is proposed to effectively address the negative effect of various model uncertainties and external disturbances. In order to facilitate the control parameter selection, a gain tuning method is also presented. Comparative simulations are carried out, which indicate that the proposed two-level interaction force controller achieves smaller interaction force and better robust performance to various modeling errors and disturbances.

Design and Development of An Instrumented Knee Joint for Quantifying Ligament Displacements

Abstract Recently, robotic assistive leg exoskeletons have gained popularity because an increased number of people crave for powered devices to run faster and longer or carry heavier loads. However, these powered devices have the potential to impair knee ligaments. This work was aimed to develop an instrumented knee joint via rapid prototyping that measures the displacements of the four major knee ligaments—the anterior cruciate ligament (ACL), posterior crucial ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL)—to quantify the strain experienced by these ligaments. The knee model consists of a femur, lateral and medial menisci, and a tibia-fibula, which were printed from three dimensional (3D) imaging scans. Nonstretchable cords served as main fiber bundles of the ligaments with their desired stiffnesses provided by springs. The displacement of each cord was obtained via a rotary encoder mechanism, and the leg flexion angle was acquired via a closed-loop four-bar linkage of a diamond shape. The displacements were corroborated by published data, demonstrating the profiles of the displacement curves agreed with known results. The paper shows the feasibility of developing a subject-specific knee joint via rapid prototyping that is capable of quantifying the ligament strain via rapid prototyping.

Stress-strain Test of Exoskeleton Legs Based on Different Postures

Aiming at the design requirements of high-strength and lightweight of exoskeleton leg materials, this paper designs a kind of exoskeleton leg mechanism made of T700 carbon fiber and TC4 titanium alloy. The mechanical properties of exoskeleton leg mechanism under three different postures of standing, stranding and squatting were tested by DH5921 dynamic strain gauge. The results showed that the maximum stress and strain were located at the ankle auricular part under three typical postures, and the maximum stress was 150.7MPa. The maximum strain value of the T700 composite material in the middle of the thigh is 848.05με, which meets the requirements of use. In the three different postures, the stress value of each place in the squatting posture increases obviously, but it is still far less than the required strength of the design material, and meets the requirements of use.

Fatigue performance test of exoskeleton leg component based on composite materials

In order to meet the requirements of lightweight structure design of exoskeleton robot, this paper proposes a T700 carbon fiber exoskeleton leg component based on composite material. By analyzing the function and characteristic of the leg component, a new kind of leg component combined with titanium alloy and T700 carbon fiber was designed. The fatigue performance of the new leg component was tested. The results show that no fatigue failure occurs when the leg component are repeatedly loaded 50 times in the direction of 90° and 45° and the loading force is 2000N. The failure tensile test shows that when the loading load reaches 1700N, fracture failure occurs and the connection interface is destroyed.

Design and Preliminary Assessment of a Passive Elastic Leg Exoskeleton for Resistive Gait Rehabilitation

This article aimed to develop a unique exoskeleton to provide different types of elastic resistances (i.e., resisting flexion, extension, or bidirectionally) to the leg muscles during walking. We created a completely passive leg exoskeleton, consisting of counteracting springs, pulleys, and clutches, to provide different types of elastic resistance to the knee. We first used a benchtop setting to calibrate the springs and validate the resistive capabilities of the device. We then tested the device's ability to alter gait mechanics, muscle activation, and kinematic aftereffects when walking on a treadmill under the three resistance types. Benchtop testing indicated that the device provided a nearly linear torque profile and could be accurately configured to alter the angle where the spring system was undeformed (i.e., the resting position). Treadmill testing indicated the device could specifically target knee flexors, extensors, or both, and increase eccentric loading at the joint. Additionally, these resistance types elicited different kinematic aftereffects that could be used to target user-specific spatiotemporal gait deficits. These results indicate that the elastic device can provide various types of targeted resistance training during walking. The proposed elastic device can provide a diverse set of resistance types that could potentially address user-specific muscle weaknesses and gait deficits through functional resistance training.

Precision Interaction Force Control of an Underactuated Hydraulic Stance Leg Exoskeleton Considering the Constraint from the Wearer

Hydraulic lower limb exoskeletons are wearable robotic systems, which can help people carry heavy loads. Recently, underactuated exoskeletons with some passive joints have been developed in large numbers for the purpose of decreasing the weight and energy consumption of the system. There are many control algorithms for a multi-joint fully actuated exoskeleton, which cannot be applied for underactuated systems due to the reduction in the number of control inputs. Besides, since the hydraulic actuator is not a desired force output source, there exist high order nonlinearities in hydraulic exoskeletons, which makes the controller design more challenging than motor driven exoskeleton systems. This paper proposed a precision interaction force controller for a 3DOF underactuated hydraulic stance leg exoskeleton. First, the control effect of the wearer is considered and the posture of the exoskeleton back is assumed as a desired trajectory under the control of the wearer. Under this assumption, the system dynamics are changed from a 3DOF underactuated system in joint space to a 2DOF fully actuated system in Cartesian space. Then, a three-level interaction force controller is designed in which the high-level controller conducts human motion intent inference, the middle level controller tracks human motion and the low-level controller achieves output force tracking of hydraulic cylinders. The MIMO adaptive robust control algorithm is applied in the controller design to effectively address the high order nonlinearities of the hydraulic system, multi-joint couplings and various model uncertainties. A gain tuning method is also provided to facilitate the controller gains selection for engineers. Comparative simulations are conducted, which demonstrate that the principal human-machine interaction force components can be minimized and good robust performance to load change and modeling errors can be achieved.

Stiffness modulation of a cable-driven leg exoskeleton for effective human–robot interaction

AbstractWith the widespread development of leg exoskeletons to provide external force-based repetitive training for gait rehabilitation, the prospect of undesired movement adaptation due to applied forces and imposed constraints require adequate investigation. A cable-driven leg exoskeleton, CDLE, presents a lightweight, flexible, and redundantly actuated architecture that enables the possibility of system parameters modulation to alter human–robot interaction while applying the desired forces. In this work, multi-joint stiffness performance of CDLE is formulated to systematically analyze human–CDLE interaction. Further, potential alterations in CDLE architecture are presented to tune human–CDLE interaction that favors the desired human leg movement during a gait rehabilitation paradigm.