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 Further, some concluding remarks are withdrawn which could be useful for future work.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

Robotic design and modelling of medical lower extremity exoskeletons

This study aims to explain the development of the robotic Lower Extremity Exoskeleton (LEE) systems between 1960 and 2019 in chronological order. The scans performed in the exoskeleton system’s design have shown that a modeling program, such as AnyBody, and OpenSim, should be used first to observe the design and software animation, followed by the mechanical development of the system using sensors and motors. Also, the use of OpenSim and AnyBody musculoskeletal system software has been proven to play an essential role in designing the human-exoskeleton by eliminating the high costs and risks of the mechanical designs. Furthermore, these modeling systems can enable rapid optimization of the LEE design by detecting the forces and torques falling on the human muscles

Non-linear actuators and simulation tools for rehabilitation devices

Mención Internacional en el título de doctorRehabilitation robotics is a field of research that investigates the applications of robotics in motor function therapy for recovering the motor control and motor capability. In general, this type of rehabilitation has been found effective in therapy for persons suffering motor disorders, especially due to stroke or spinal cord injuries. This type of devices generally are well tolerated by the patients also being a motivation in rehabilitation therapy. In the last years the rehabilitation robotics has become more popular, capturing the attention at various research centers. They focused on the development more effective devices in rehabilitation therapy, with a higher acceptance factor of patients tacking into account: the financial cost, weight and comfort of the device. Among the rehabilitation devices, an important category is represented by the rehabilitation exoskeletons, which in addition to the human skeletons help to protect and support the external human body. This became more popular between the rehabilitation devices due to the easily adapting with the dynamics of human body, possibility to use them such as wearable devices and low weight and dimensions which permit easy transportation. Nowadays, in the development of any robotic device the simulation tools play an important role due to their capacity to analyse the expected performance of the system designed prior to manufacture. In the development of the rehabilitation devices, the biomechanical software which is capable to simulate the behaviour interaction between the human body and the robotics devices, play an important role. This helps to choose suitable actuators for the rehabilitation device, to evaluate possible mechanical designs, and to analyse the necessary controls algorithms before being tested in real systems. This thesis presents a research proposing an alternative solution for the current systems of actuation on the exoskeletons for robotic rehabilitation. The proposed solution, has a direct impact, improving issues like device weight, noise, fabrication costs, size an patient comfort. In order to reach the desired results, a biomechanical software based on Biomechanics of Bodies (BoB) simulator where the behaviour of the human body and the rehabilitation device with his actuators can be analysed, was developed. In the context of the main objective of this research, a series of actuators have been analysed, including solutions between the non-linear actuation systems. Between these systems, two solutions have been analysed in detail: ultrasonic motors and Shape Memory Alloy material. Due to the force - weight characteristics of each device (in simulation with the human body), the Shape Memory Alloy material was chosen as principal actuator candidate for rehabilitation devices. The proposed control algorithm for the actuators based on Shape Memory Alloy, was tested over various configurations of actuators design and analysed in terms of energy eficiency, cooling deformation and movement. For the bioinspirated movements, such as the muscular group's biceps-triceps, a control algorithm capable to control two Shape Memory Alloy based actuators in antagonistic movement, has been developed. A segmented exoskeleton based on Shape Memory Alloy actuators for the upper limb evaluation and rehabilitation therapy was proposed to demosntrate the eligibility of the actuation system. This is divided in individual rehabilitation devices for the shoulder, elbow and wrist. The results of this research was tested and validated in the real elbow exoskeleton with two degrees of freedom developed during this thesis.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Eduardo Rocón de Lima.- Secretario: Concepción Alicia Monje Micharet.- Vocal: Martin Stoele

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%

Robot Assisted Shoulder Rehabilitation: Biomechanical Modelling, Design and Performance Evaluation

The upper limb rehabilitation robots have made it possible to improve the motor recovery in stroke survivors while reducing the burden on physical therapists. Compared to manual arm training, robot-supported training can be more intensive, of longer duration, repetitive and task-oriented. To be aligned with the most biomechanically complex joint of human body, the shoulder, specific considerations have to be made in the design of robotic shoulder exoskeletons. It is important to assist all shoulder degrees-of-freedom (DOFs) when implementing robotic exoskeletons for rehabilitation purposes to increase the range of motion (ROM) and avoid any joint axes misalignments between the robot and human’s shoulder that cause undesirable interaction forces and discomfort to the user. The main objective of this work is to design a safe and a robotic exoskeleton for shoulder rehabilitation with physiologically correct movements, lightweight modules, self-alignment characteristics and large workspace. To achieve this goal a comprehensive review of the existing shoulder rehabilitation exoskeletons is conducted first to outline their main advantages and disadvantages, drawbacks and limitations. The research has then focused on biomechanics of the human shoulder which is studied in detail using robotic analysis techniques, i.e. the human shoulder is modelled as a mechanism. The coupled constrained structure of the robotic exoskeleton connected to a human shoulder is considered as a hybrid human-robot mechanism to solve the problem of joint axes misalignments. Finally, a real-scale prototype of the robotic shoulder rehabilitation exoskeleton was built to test its operation and its ability for shoulder rehabilitation

Design and Control of a Knee Exoskeleton for Assistance and Power Augmentation

Thanks to the technological advancements, assistive lower limb exoskeletons are moving from laboratory settings to daily life scenarios. This dissertation makes a contribution toward the development of assistive/power augmentation knee exoskeletons with an improved wearability, ergonomics and intuitive use. In particular, the design and the control of a novel knee exoskeleton system, the iT-Knee Bipedal System, is presented. It is composed by: a novel mechanism to transmit the assistance generated by the exoskeleton to the knee joint in a more ergonomic manner; a novel method that requires limited information to estimate online the torques experienced by the ankles, knees and hips of a person wearing the exoskeleton; a novel sensor system for shoes able to track the feet orientation and monitor their full contact wrench with the ground. In particular, the iT-Knee exoskeleton, the main component of the aforementioned system, is introduced. It is a novel six degree of freedom knee exoskeleton module with under-actuated kinematics, able to assist the flexion/extension motion of the knee while all the other joint\u2019s movements are accommodated. Thanks to its mechanism, the system: solves the problem of the alignment between the joint of the user and the exoskeleton; it automatically adjusts to different users\u2019 size; reduces the undesired forces and torques exchanged between the attachment points of its structure and the user\u2019s skin. From a control point of view, a novel approach to address difficulties arising in real life scenarios (i.e. noncyclic locomotion activity, unexpected terrain or unpredicted interactions with the surroundings) is presented. It is based on a method that estimates online the torques experienced by a person at his ankles, knees and hips with the major advantage that does not rely on any information of the user\u2019s upper body (i.e. pose, weight and center of mass location) or on any interaction of the user\u2019s upper body with the environment (i.e. payload handling or pushing and pulling task). This is achieved v by monitoring the full contact wrench of the subject with the ground and applying an inverse dynamic approach to the lower body segments. To track the full contact wrench between the subject\u2019s feet and the ground, a novel add on system for shoes has been developed. The iT-Shoe is adjustable to different user\u2019s size and accommodates the plantar flexion of the foot. It tracks the interactions and the orientation of the foot thanks to two 6axis Force/Torque sensors, developed in-house, with dedicated embedded MEMS IMUs placed at the toe and heel area. Different tasks and ground conditions were tested to validate and highlight the potentiality of the proposed knee exoskeleton system. The experimental results obtained and the feedback collected confirm the validity of the research conducted toward the design of more ergonomic and intuitive to use exoskeletons

Low obstacles avoidance for lower limb exoskeletons

Gli esoscheletri motorizzati per gli arti inferiori (LLEs) sono robot indossabili che permettono a soggetti con disabilità degli arti inferiori di camminare indipendentemente, e persino migliorare le prestazioni degli arti inferiori nel caso di soggetti sani. Nonostante i recenti sviluppi, l'uso di questa promettente tecnologia è relegato agli ambiti clinici e di ricerca; il suo utilizzo come strumento per camminare in modo indipendente in ambienti non controllati è ancora mancante. Il motivo principale di questa limitazione è dovuto alla mancanza di adattabilità degli LLE ai diversi ambienti che possono essere incontrati durante il cammino: la maggioranza degli LLE sfrutta traiettorie predefinite degli arti inferiori senza valutare l'ambiente circostante. Questo implica che ogni tipo di controllo addizionale è a carico dell'utente, e risulta in un sovraccarico fisico e cognitivo da parte di quest'ultimo. Questa tesi si pone l'obbiettivo di superare le limitazioni sopracitate, proponendo un approccio innovativo per aumentare l'autonomia degli LLE. In particolare, il metodo proposto ha lo scopo di stimare la traiettoria degli arti inferiori ottimale, così da poter superare in modo autonomo gli ostacoli bassi che potrebbero essere incontrati lungo il cammino. Tramite l'uso di una stereo camera unita ad un algoritmo di Computer Vision, l'ambiente viene percepito in modo da identificare il pavimento e gli ostacoli che potrebbero influenzare il cammino con l'obbiettivo di selezionare il punto d'appoggio ottimale per il piede. Successivamente, un algoritmo iterativo per la generazione della traiettoria del piede senza collisioni (CFFTG) permette di ottenere i dati necessari a calcolare la cinematica inversa dell'esoscheletro, ed infine gli angoli ai giunti ottenuti da quest'ultima vengono forniti ai controllori dei motori per effettuare il movimento desiderato. Test sperimentali in simulazione (basati su dati reali) sono stati eseguiti per valutare il comportamento dell'algoritmo di Computer Vision e del CFFTG, mostrando ottimi risultati in diversi scenari. Inoltre, le assunzioni su cui si basa la soluzione proposta permettono la sua compatibilità con la maggioranza degli esoscheletri commerciali e di ricerca attualmente disponibili. Credo che pensare agli esoscheletri come degli agenti semi autonomi, piuttosto che come dei dispositivi controllati unicamente dall'utente, rappresenti non solo un percorso che porterà alla simbiosi tra uomo ed esoscheletro, ma anche all'uso di questa tecnologia nella vita di tutti i giorni.Powered lower limb exoskeletons (LLEs) are innovative wearable robots that allow independent walking in people with severe gait impairments, or even to augment lower limb capabilities of able-bodied users. Despite the recent advancements, the use of this promising technology is still restricted to controlled research/clinical settings; uptake in real-life conditions as a device to promote user independence is still lacking. The main reason behind this limitation can be traced back to the lack adaptability of LLEs to the different walking conditions that may be encountered in real world settings: the majority of LLEs relies on predefined gait trajectories and is generally unaware of the environment in which gait occurs. This means that the control burden is entirely on the user, resulting in an increased physical and cognitive workload. This thesis aims at overcoming the aforementioned limitations by proposing a novel approach to enhance the autonomy of the LLEs. In particular, the proposed method has the purpose of estimating the optimal gait trajectory of the exoskeleton in order to autonomously avoid low obstacles on the ground. By using a depth camera coupled with Computer Vision software module, the environment is sensed to detect the ground plane and obstacles that might interfere with the forward motion, in order to predict the following foothold. Then, an iterative-based collision-free foot trajectory generator (CFFTG) algorithm is proposed to calculate the optimal foot motion and the joints’ angles to be sent to the exoskeleton low-level controllers. Experimental tests have been carried out in simulation to evaluate both the CV module and the CFFTG based on real data, showing successful performance in different scenarios. In addition, the assumptions that have been considered in this work make the proposed approach compatible with the majority of exoskeletons in research and on the market. I believe that re-thinking exoskeletons as semi-autonomous agents will represent not only the cornerstone to promote a more symbiotic human-exoskeleton interaction but may also pave the way for the use of this technology in the everyday life

Otimização muscle-in-the-loop em tempo real para reabilitação física com um exosqueleto ativo: uma mudança de paradigma

Assisting human locomotion with a wearable robotic orthosis is still quite challenging, largely due to the complexity of the neuromusculoskeletal system, the time-varying dynamics that accompany motor adaptation, and the uniqueness of every individual’s response to the assistance given by the robot. To this day, these devices have not met their well-known promise yet, mostly due to the fact that they are not perfectly suitable for the rehabilitation of neuropathologic patients. One of the main challenges hampering this goal still relies on the interface and co-dependency between the human and the machine. Nowadays, most commercial exoskeletons replay pre-defined gait patterns, whereas research exoskeletons are switching to controllers based on optimized torque profiles. In most cases, the dynamics of the human musculoskeletal system are still ignored and do not take into account the optimal conditions for inducing a positive modulation of neuromuscular activity. This is because both rehabilitation strategies are still emphasized on the macro level of the whole joint instead of focusing on the muscles’ dynamics and activity, which are the actual anatomical elements that may need to be rehabilitated. Strategies to keep the human in the loop of the exoskeleton’s control laws in real-time may help to overcome these challenges. The main purpose of the present dissertation is to make a paradigm shift in the approach on how the assistance that is given to a subject by an exoskeleton is modelled and controlled during physical rehabilitation. Therefore, in the scope of the present work, it was intended to design, concede, implement, and validate a real-time muscle-in-the-loop optimization model to find the best assistive support ratio that would induce optimal rehabilitation conditions to a specific group of impaired muscles while having a minimum impact on the other healthy muscles. The developed optimization model was implemented in the form of a plugin and was integrated on a neuromechanical model-based interface for driving a bilateral ankle exoskeleton. Experimental pilot tests evaluated the feasibility and effectiveness of the model. Results of the most significant pilots achieved EMG reductions up to 61 ± 3 % in Soleus and 41 ± 10 % in Gastrocnemius Lateralis. Moreover, results also demonstrated the efficiency of the optimization’s specific reduction on rehabilitation by looking into the muscular fatigue after each experiment. Finally, two parallel preliminary studies emerged from the pilots, which looked at muscle adaptation, after a new assistive condition had been applied, over time and at the effect of the lateral positioning of the exoskeleton’s actuators on the leg muscles.Auxiliar a locomoção humana com uma ortose robótica ainda é bastante desafiante, em grande parte devido à complexidade do sistema neuromusculoesquelético, à dinâmica variável no tempo que acompanha a adaptação motora e à singularidade da resposta de cada indivíduo à assistência dada pelo robô. Até hoje, está por cumprir a promessa inicial destes dispositivos, principalmente devido ao facto de não serem perfeitamente adequados para a reabilitação de pacientes neuropatológicos. Um dos principais desafios que dificultam esse objetivo foca-se ainda na interface e na co-dependência entre o ser humano e a máquina. Hoje em dia, a maioria dos exoesqueletos comerciais reproduz padrões de marcha predefinidos, enquanto que os exoesqueletos em investigação estão só agora a mudar para controladores com base em perfis de binário otimizados. Na maioria dos casos, a dinâmica do sistema musculoesquelético humano ainda é ignorada e não tem em consideração as condições ideais para induzir uma modulação positiva da atividade neuromuscular. Isso ocorre porque ambas as estratégias de reabilitação ainda são enfatizadas no nível macro de toda a articulação, em vez de se concentrar na dinâmica e atividade dos músculos, que são os elementos anatómicos que realmente precisam de ser reabilitados. Estratégias para manter o ser humano em loop nos comandos que controlam o exoesqueleto em tempo real podem ajudar a superar estes desafios. O principal objetivo desta dissertação é fazer uma mudança de paradigma na abordagem em como a assistência que é dada a um sujeito por um exosqueleto é modelada e controlada durante a reabilitação física. Portanto, no contexto do presente trabalho, pretendeu-se projetar, conceder, implementar e validar um modelo de otimização muscle-in-the-loop em tempo real para encontrar a melhor relação de suporte capaz de induzir as condições ideais de reabilitação para um grupo específico de músculos fragilizados, tendo um impacto mínimo nos outros músculos saudáveis. O modelo de otimização desenvolvido foi implementado na forma de um plugin e foi integrado numa interface baseada num modelo neuromecânico para o controlo de um exoesqueleto bilateral de tornozelo. Testes experimentais piloto avaliaram a viabilidade e a eficácia do modelo. Os resultados dos testes mais significativos demonstraram reduções de EMG de até 61 ± 3 % no Soleus e 41 ± 10 % no Gastrocnemius Lateral. Adicionalmente, os resultados demonstraram também a eficiência em reabilitação da redução específica no EMG devido à otimização tendo em conta a fadiga muscular após cada teste. Finalmente, dois estudos preliminares paralelos emergiram dos testes piloto, que analisaram a adaptação muscular após uma nova condição assistiva ter sido definida ao longo do tempo e o efeito do posicionamento lateral dos atuadores do exoesqueleto nos músculos da perna.Mestrado em Engenharia Biomédic