Design and control of a single-leg exoskeleton with gravity compensation for children with unilateral cerebral palsy

Children with cerebral palsy (CP) experience reduced quality of life due to limited mobility and independence. Recent studies have shown that lower-limb exoskeletons (LLEs) have significant potential to improve the walking ability of children with CP. However, the number of prototyped LLEs for children with CP is very limited, while no single-leg exoskeleton (SLE) has been developed specifically for children with CP. This study aims to fill this gap by designing the first size-adjustable SLE for children with CP aged 8 to 12, covering Gross Motor Function Classification System (GMFCS) levels I to IV. The exoskeleton incorporates three active joints at the hip, knee, and ankle, actuated by brushless DC motors and harmonic drive gears. Individuals with CP have higher metabolic consumption than their typically developed (TD) peers, with gravity being a significant contributing factor. To address this, the study designed a model-based gravity-compensator impedance controller for the SLE. A dynamic model of user and exoskeleton interaction based on the Euler–Lagrange formulation and following Denavit–Hartenberg rules was derived and validated in Simscape™ and Simulink® with remarkable precision. Additionally, a novel systematic simplification method was developed to facilitate dynamic modelling. The simulation results demonstrate that the controlled SLE can improve the walking functionality of children with CP, enabling them to follow predefined target trajectories with high accuracy

Design and Control of a Single-Leg Exoskeleton with Gravity Compensation for Children with Unilateral Cerebral Palsy

Children with cerebral palsy (CP) experience reduced quality of life due to limited mobility and independence. Recent studies have shown that lower-limb exoskeletons (LLEs) have significant potential to improve the walking ability of children with CP. However, the number of prototyped LLEs for children with CP is very limited, while no single-leg exoskeleton (SLE) has been developed specifically for children with CP. This study aims to fill this gap by designing the first size-adjustable SLE for children with CP aged 8 to 12, covering Gross Motor Function Classification System (GMFCS) levels I to IV. The exoskeleton incorporates three active joints at the hip, knee, and ankle, actuated by brushless DC motors and harmonic drive gears. Individuals with CP have higher metabolic consumption than their typically developed (TD) peers, with gravity being a significant contributing factor. To address this, the study designed a model-based gravity-compensator impedance controller for the SLE. A dynamic model of user and exoskeleton interaction based on the Euler–Lagrange formulation and following Denavit–Hartenberg rules was derived and validated in Simscape™ and Simulink® with remarkable precision. Additionally, a novel systematic simplification method was developed to facilitate dynamic modelling. The simulation results demonstrate that the controlled SLE can improve the walking functionality of children with CP, enabling them to follow predefined target trajectories with high accuracy

Innovation in augmenting hip and ankle performance during walking

This thesis considers two topics: hip assistance using a powered exoskeleton, and ankle assistance using a passive ankle-foot orthosis during walking. Part A introduces a lightweight bilateral hip exoskeleton used for improving gait function. Part B introduces an adjustable ankle foot orthosis to assist with ankle correction.Exoskeletons are wearable robotic devices that can assist with a variety of tasks, such as load carrying, walking, or rehabilitation. In Part A, I introduce an ultra-lightweight hip exoskeleton aimed at assisting individuals with Cerebral Palsy and other gait impairments during rehabilitation or gait training exercises. This thesis presents the mechanical design and validation of the exoskeleton. The final mechanical design of the hip exoskeleton was derived through several prototypes, and verified for specific engineering requirements: weight, torque application, range of motion, and user comfort. A summary of the hip exoskeleton control system is briefly discussed. Ankle-foot orthoses (AFOs) are devices commonly utilized for gait correction. AFOs are boot-like structures that encase the foot and lower leg to provide extra support and stability to the user during everyday tasks. Current market AFOs are extremely rigid, making walking difficult for individuals due to reduced ankle movement. Part B of this thesis introduces an adjustable AFO to help individuals increase their ankle motion while also aiding ankle power during stance and swing phases of the gait cycle. The final design of the AFO was derived through a single prototype, and validated for specific engineering requirements: weight, spring stiffness, modification ability, range of motion, and comfort

Psychological and care impact of the daily use of a pediatric gait exoskeleton in children with spinal muscular atrophy

Introducción: La Atrofia Muscular Espinal Tipo II, es una enfermedad neurodegenerativa de origen genético que cursa con debilidad muscular y provoca deterioro motor e incapacidad para caminar en los niños. Se relaciona con graves problemas respiratorios, musculoesqueléticos, gastrointestinales y otros de salud y cuidado. Los exoesqueletos robóticos de miembros inferiores son dispositivos médicos que ayudan a la marcha de pacientes que no pueden caminar. Nuestro objetivo fue evaluar el impacto en la dimensión psicológica y de autocuidado derivado del uso del exoesqueleto ATLAS en el hogar en niños con Atrofia Muscular Espinal Tipo II. Metodología: tres niños con Atrofia Muscular Espinal Tipo II utilizaron el exoesqueleto en casa cinco días a la semana durante un período de dos meses para caminar y realizar actividades. Se realizó una evaluación del autocuidado de enfermería antes y durante el uso del dispositivo para evaluar los cambios en los resultados del autocuidado y los diagnósticos de enfermería. Se realizaron entrevistas en profundidad y semiestructuradas, además de la observación durante las sesiones, para evaluar el impacto de la experiencia en la dimensión psicológica de los participantes. Resultados: el uso del exoesqueleto produjo cambios en los condicionantes básicos de los niños y una mejora en los organismos de autocuidado. También aparecieron nuevas demandas de autocuidado. Tres de los diez diagnósticos de enfermería fueron resueltos. Asimismo, los niños mostraron una buena tolerancia a la actividad además de una mejora funcional evaluada en el tercer participante. Los niños y los cuidadores principales valoraron la experiencia como positiva y significativa. Los niños tenían una mayoría de emociones positivas, y se incrementó su autonomía y comportamiento social y exploratorio. Conclusiones: la tecnología del exoesqueleto podría considerarse como un nuevo recurso para el cuidado de niños con enfermedades neuromusculares. Su uso tuvo un impacto positivo tanto en las variables de autocuidado como en la dimensión psicológica de tres niños con atrofia muscular espinal tipo II. Aunque este estudio aporta ya evidencia, más estudios sobre el tema aportarían un mayor conocimiento

Transient Thermal Analysis of a Magnetorheological Knee for Prostheses and Exoskeletons during Over-Ground Walking

Proper knee movement is essential for accomplishing the mobility daily tasks such as walking, get up from a chair and going up and down stairs. Although the technological advances in active knee actuators for prostheses and exoskeletons to help impaired people in the last decade, they still present several usage limitations such as overweight or limited mechanical power and torque. To address such limitations, we developed the Active Magnetorheological Knee (AMRK) that comprises a Motor Unit (MU), which is a motor-reducer (EC motor and Harmonic Drive) and a MR clutch, that works in parallel to a magnetorheological (MR) brake. Magnetorheological fluids, employed in the MR clutch and brake, are smart materials that have their rheological properties controlled by an induced magnetic field and have been used for different purposes. With this configuration the actuator can work as a motor, clutch or brake and can perform similar movements than a healthy knee. However, the stability, control, and life of magnetorheological fluids critically depend on the working temperature. By reaching a certain temperature limit, the fluid additives quickly deteriorate, leading to irreversible changes of the MR fluid. In this study, we perform a transient thermal analysis of the AMRK, when it is used for walking over-ground, to access possible fluid degradation and user’s discomfort due overheating. The resulting shear stress in the MR clutch and brake generates heat, increasing the fluid temperature during the operation. However, to avoid overheating, we proposed a mode of operation for over-ground walking aiming to minimize the heat generation on the MR clutch and brake. Other heat sources inside the actuator are the coils, which generate the magnetic fields for the MR fluid, bearings, EC motor and harmonic drive. Results show that the MR fluid of the brake can reach up to 31°C after a 6.0 km walk, so the AMRK can be used for the proposed function without risks of fluid degradation or discomfort for the user