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

Design and Development of a Lightweight Ankle Exoskeleton for Human Walking Augmentation

RESUMÉ La plupart des exosquelettes motorisés de la cheville ont une masse distale considérable, ce qui limite leur capacité à réduire l’énergie dépensée par l’utilisateur durant la marche. L’objectif de notre travail est de développer un exosquelette de chevilles avec le minimum de masse distale ajoutée comparé aux exosquelettes motorisés de chevilles existants. Aussi, l’exosquelette doit fournir au moins 50 Nm de support au couple de flexion plantaire. L’exosquelette développé dans le cadre de ce mémoire utilise deux câbles Bowden pour transmettre la force mécanique de l’unité d’actionnement attachée à la taille aux deux tiges en fibre de Carbonne attachées à la botte de l’utilisateur. Quand les deux tiges sont tirées, ils génèrent un couple qui supporte le mouvement de flexion plantaire à la fin de la phase d’appui du cycle de marche. Une pièce conçue sur mesure et imprimé en plastique par prototypage rapide a été attachée au tibia pour ajuster la direction des câbles. Une étude d’optimisation a été effectuée pour minimiser la masse des tiges limitant ainsi la masse distale de l’exosquelette (attaché au tibia et pied) à seulement 348 g. Le résultat principal obtenu à partir des tests de marche est la réduction de l’activité des muscles soléaire et gastrocnémien du sujet par une moyenne de 37% et 44% respectivement lors de la marche avec l’exosquelette comparée à la marche normale. Cette réduction s’est produite quand l’exosquelette a fourni une puissance mécanique de 19 ± 2 W avec un actionnement qui a commencé à 38% du cycle de marche. Ce résultat démontre le potentiel de notre exosquelette à réduire le cout métabolique de marche et souligne l’importance de réduire la masse distale d’un exosquelette de marche.----------ABSTRACT Most of powered ankle exoskeletons add considerable distal mass to the user which limits their capacity to reduce the metabolic energy of walking. The objective of the work presented in this master thesis is to develop an ankle exoskeleton with a minimum added distal mass compared to existing autonomous powered ankle exoskeletons, while providing at least 50 Nm of assistive plantar flexion torque. The exoskeleton developed in this master thesis uses Bowden cables to transmit the mechanical force from the actuation unit attached to the waist to the carbon fiber struts fixed on the boot. As the struts are pulled, they create an assistive ankle plantar flexion torque. A 3D-printed brace was attached to the shin to adjust the direction of the cables. A design optimization study was performed to minimize the mass of the struts, thereby limiting the total added distal mass, attached to the shin and foot, to only 348 g. The main result obtained from walking tests was the reduction of the soleus and gastrocnemius muscles activity by an average of 37% and 44% respectively when walking with the exoskeleton compared to normal walking. This reduction occurred when the exoskeleton delivered a mechanical power of 19 ± 2 W with an actuation onset fixed at 38% of the gait cycle. This result shows the potential of the proposed exoskeleton to reduce the metabolic cost of walking and emphasizes the importance of minimizing the distal mass of ankle exoskeletons

Basic functionality of a prototype wearable assistive soft exoskeleton for people with gait impairments : a case study

XoSoft is a soft modular wearable assistive exoskeleton for peo- ple with mild to moderate gait impairments. It is currently being developed by a European Consortium (www.xosoft.eu) and aims to provide tailored and active lower limb support during ambu- lation. During development, user-centered design principles were followed in parallel with the aim of providing functional support during gait. A prototype was developed and was tested for practi- cability, usability, comfort and assistive function (summarized as basic functionality) with a potential end user. The prototype con- sisted of a garment, electromagnetic clutch-controlled elastic bands supporting knee- and hip flexion and a backpack containing the sensor and actuator control of the system. The participant had ex- perienced a stroke and presented with unilateral impairment of the lower and upper extremities. In testing, he donned and doffed the prototype independently as far as possible, and performed walk- ing trials with the system in both active (powered on) and pas- sive (powered off) modes. Afterwards, the participant rated the perceived pressure and various elements of usability. Results high- lighted aspects of the system for improvement during future phases of XoSoft development, and also identified useful aspects of proto- type design to be maintained. The basic functionality of XoSoft could be assumed as satisfactory given that it was the first version of a working prototype. The study highlights the benefits of this participatory evaluation design approach in assistive soft robotics development

Design and Evaluation of Elastic Exoskeletons for Human Running

Humans bounce along the ground when they hop and run, providing spring-like function with their muscles and tendons. Compliant elastic mechanisms could assist this motion by contributing additional elastic storage and return. This in turn would decrease the demands on the human leg, making it easier to hop or run. I developed an elastic knee brace and an elastic lower limb exoskeleton that add parallel stiffness to the human knee joint and entire leg, respectively. The objective of this dissertation was to determine how humans are affected by the parallel elasticity when they hop and run. In the elastic knee orthosis study, ten subjects hopped on one leg with and without stiffness added in parallel to the knee. The mean brace stiffness was 5.6 N-m/◦, effectively 31.5% of total knee stiffness when hopping in this condition. When subjects hopped at fixed (2.2 Hz) and preferred frequencies, knee extensor muscle activation levels and biological knee stiffness decreased (P < .05). This indicated that elastic knee exoskeletons could be effective at reducing the metabolic cost of locomotion in bouncing gaits. However, this study also identified critical shortcomings to a joint-based approach for exoskeletons that assist running. The elastic whole limb exoskeleton was used to explore effects of adding parallel leg elasticity with a non-joint-based system. Six subjects ran with and without the exoskeleton at 2.3 m/s. While running in the exoskeleton there was a significant increase in metabolic cost as well as hip flexor and extensor muscle activation levels during the swing phase (P < .0001). The exoskeleton was designed to provide 30-50% of leg stiffness in two conditions. While running, the exoskeleton provided only 18.4% and 19.2% of leg stiffness, and only 7.0% and 7.2% of the peak vertical force transmitted to the ground. This discrepancy was due to motion of the exoskeleton waist harness on subjects and controller functionality. This dissertation provides clear suggestions for design of future exoskeletons that could assist with human running. It is expected that future devices that build on the successes of these prototypes will benefit healthy individuals and those with decreased muscle function.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75905/1/mscherry_1.pd

Back-Support Exoskeletons for Occupational Use: An Overview of Technological Advances and Trends

OCCUPATIONAL APPLICATIONSMany new occupational back-support exoskeletons have been developed in the past few years both as research prototypes and as commercial products. These devices are intended..

Preliminary design and control of a soft exosuit for assisting elbow movements and hand grasping in activities of daily living

The development of a portable assistive device to aid patients affected by neuromuscular disorders has been the ultimategoal of assistive robots since the late 1960s. Despite significant advances in recent decades, traditional rigid exoskeletonsare constrained by limited portability, safety, ergonomics, autonomy and, most of all, cost. In this study, we present thedesign and control of a soft, textile-based exosuit for assisting elbow flexion/extension and hand open/close. We describea model-based design, characterisation and testing of two independent actuator modules for the elbow and hand,respectively. Both actuators drive a set of artificial tendons, routed through the exosuit along specific load paths, thatapply torques to the human joints by means of anchor points. Key features in our design are under-actuation and the useof electromagnetic clutches to unload the motors during static posture. These two aspects, along with the use of 3Dprinted components and off-the-shelf fabric materials, contribute to cut down the power requirements, mass and overallcost of the system, making it a more likely candidate for daily use and enlarging its target population. Low-level control isaccomplished by a computationally efficient machine learning algorithm that derives the system’s model from sensorydata, ensuring high tracking accuracy despite the uncertainties deriving from its soft architecture. The resulting system isa low-profile, low-cost and wearable exosuit designed to intuitively assist the wearer in activities of daily living

Exoskeleton for ankle joint flexion/extension rehabilitation

Este trabajo presenta el modelado, diseño, construcción, y control de un exoesqueleto para rehabilitación de la flexión/extensión de la articulación del tobillo. El modelo dinámico de la flexión/extensión del tobillo es obtenido por medio de la formulación de Euler-Lagrange y es construido en Simulink de MATLAB usando la ecuación diferencial no-lineal derivada del análisis dinámico. Un controlador PID de realimentación del desplazamiento angular, representando el control neuromusculoesquelético humano, es implementado en el modelo dinámico para estimar el torque articular requerido durante los movimientos del tobillo. Se realizan simulaciones en el modelo para el rango de movimiento (ROM) de la flexión/extensión del tobillo, y los resultados son usados para seleccionar el actuador más adecuado para el exoesqueleto. El exoesqueleto para rehabilitación del tobillo es diseñado en el software CAD SolidWorks, construido por impresión 3D en ácido poliláctico (PLA), accionado por dos servomotores que entregan juntos un torque continuo máximo de 22 [kg cm], y controlado por una placa Arduino que establece comunicación Bluetooth con un aplicativo móvil desarrollado en MIT App Inventor para la programación de los parámetros de las terapias de rehabilitation. El resultado de este trabajo es un exoesqueleto liviano de tobillo, con una masa total de 0.85[kg] incluyendo actuadores (servomotores) y electrónica (microcontrolador y baterías), el cual puede ser usado en prácticas de telerehabilitación garantizando errores de seguimiento del desplazamiento angular por debajo del 10%.This work presents the modelling, design, construction, and control of an exoskeleton for ankle joint flexion/extension rehabilitation. The dynamic model of the ankle flexion/extension is obtained through Euler-Lagrange formulation and is built in Simulink of MATLAB using the non-linear differential equation derived from the dynamic analysis. An angular displacement feedback PID controller, representing the human neuromusculoskeletal control, is implemented in the dynamic model to estimate the joint torque required during ankle movements. Simulations are carried out in the model for the ankle flexion/extension range of motion (ROM), and the results are used to select the most suitable actuators for the exoskeleton. The ankle rehabilitation exoskeleton is designed in SolidWorks CAD software, built through 3D printing in polylactic acid (PLA), powered by two on-board servomotors that deliver together a maximum continuous torque of 22 [kg cm], and controlled by an Arduino board that establishes Bluetooth communication with a mobile app developed in MIT App Inventor for programming the parameters of the rehabilitation therapies. The result of this work is a lightweight ankle exoskeleton, with a total mass of 0.85 [kg] including actuators (servomotors) and electronics (microcontroller and batteries), which can be used in telerehabilitation practices guaranteeing angular displacement tracking errors under 10%

Wearable ankle assistance robot for a human walking with different loads

To reduce energy consumption while a human is walking with different loads, an active energy storage mechanism and a gait cycle prediction method are proposed, and then a wearable ankle assistance robot is developed. A motor, a clutch, and elastic rods are placed strategically in the active energy storage mechanism to achieve energy storage and release. During the period when the ankle does not generate torque, the clutch is closed, and the elastic rods are driven by the motor to produce deformation for energy storage. When the ankle generates torque, the motor is stopped and the clutch is opened, and then energy is released. Assisted force is transmitted to the human heel by a flexible transmission device to achieve walking assistance. The deformation length of the elastic rods can be changed to achieve assisted force adjustment for different loads. Based on the hip angular displacement and heel pressure, the gait cycle can be obtained with the proposed prediction method, and then assistance control can be achieved. Consequently, the development of a wearable ankle assistance robot is realized, a walking assistance experiment with different loads is completed, and the net metabolic cost is used to indicate the energy consumption. The experimental results show that the net metabolic cost of the participants is reduced by averages of 5.30 %, 5.67 %, and 4.84 % with 0, 4, and 8 kg loads respectively. The reduced net metabolic costs are compared with other research results; the reduced net metabolic costs are close to the others, but the motor power in this work is lower.</p