ESCUELA TECNICA SUPERIOR DE INGENIEROS INDUSTRIALES DEVELOPMENT OF STRATEGIES TO REDUCE ENERGY EXPENDITURE FOR LOWER-LIMB ACTIVE ORTHOSES DOCTORAL THESIS Daniel Sanz Merodio Electronic Physicist Director Dr. Elena Garcia Armada PhD Robotics and Automation, Industrial Engineer ESCUELA TECNICA SUPERIOR DE INGENIEROS INDUSTRIALES DEVELOPMENT OF STRATEGIES TO REDUCE ENERGY EXPENDITURE FOR LOWER-LIMB ACTIVE ORTHOSES DOCTORAL THESIS Daniel Sanz Merodio Electronic Physicist Director Dr. Elena Garcia Armada PhD Robotics and Automation, Industrial Engineer Madrid, September, 2018 Development of strategies to reduce energy expenditure for lower-limb active or- thoses Author: Daniel Sanz Merodio Advisor: Dr. Elena Garcia Armada First edition, August 2018 To Celsa, Gemma, Cecilia and Martina Abstract Lower-limb exoskeletons and powered orthoses are non-invasive devices that assist patients with locomotive disorders to achieve correct limb movements. The intended use as an assistive device for daily life activ- ities still encounters barriers to practical implementation. Current bat- teries cannot meet the long-term power requirements for these devices, which need to operate for long periods. This issue has become a ma- jor challenge in the development of these portable robots. Conversely, legged locomotion in animals and humans is efficient. This thesis ex- plores the methods to reduce energy consumption in the motion con- trol of gait exoskeletons and especially its applicability and feasibility. From a thorough analysis of the human gait from the energetic point of view and based on the state of development of robotics, a hybrid strategy is proposed to reduce energy consumption in the gait cycle. Three major research areas can be distinguished in energy-efficient biped walking robots: • The first research area focuses on developing optimal gait traject- ories for active walking robots. These trajectories are obtained by means of optimization procedures to minimize an objective function. • The second research area focuses on exploiting the passive-dynamics of the robot legs. In the first instance, the research is focused on non-active mechanisms that descend ramps taking advantage of the potential energy and the elastic energy of the ground contact. Subsequently, by applying these concepts, it is possible to make robots walk on flat ground providing only the amount of energy previously contributed by gravity, to take advantage of the elastic energy of the ground contact. • In the third area, leg dynamics is modified by including passive or active elastic mechanisms in the joints to reduce energy losses caused by the impact with the ground and to store and release energy for an improved energy-efficiency. In this thesis, a hybrid approach is proposed, taking advantage of the benefits of the above listed strategies to achieve an energy efficient gait. An hybrid approach is needed because gait exoskeletons applied to gait rehabilitation or assistance of people with neuromuscular dis- eases must respect the constraints imposed by the physiological needs of the patient. To solve this requirement the gait control approach must explode the natural dynamics of the leg; actively modifying joints dy- namics by the use of Variable Stiffness Actuators (VSA). By the application of a strategy of stiffness variation, control strategies based on passive dynamics can be implemented in the same joint, while the necessary torque can be provided by a stiff position controller in phases of higher torque demand, allowing subactuation in gait phases where inherent inertia is enough to take advantage of it and also provid- ing the high torque necessary for the orthosis to perform more versatile and non-cyclic movements, such as sitting and standing maneuvers. In turn, by establishing the adequate stiffness to the joint, energy con- sumption is reduced in changes of direction of the joint and energy can be stored and released in certain gait phases. The locomotion control strategies proposed have been validated through their implementation in the ATLAS active orthosis prototype. In this experiment, the importance of the variation of stiffness in relation to an efficient gait is reflected. This hybrid strategy achieves a reduction in energy consumption of 40%, while maintaining the robustness and reliability of the active orthosis with stiff actuators. The results of this research work have led to 7 publications in indexed scientific journals and 19 articles in international conferences, several of which have been awarded for their scientific and technical excel- lence. The doctoral thesis has had a relevant impact in the area of rehabilitation robotics since its results are being used in real environ- ments, since pediatric gait exoskeletons, transferred to the technology- based company Marsi Bionics, are being used in two hospitals in the therapy of neuromuscular diseases in childhood. Resumen El uso de las ortesis´ activas es cada vez mas´ habitual tanto en el campo de la rehabilitacion´ como asistencial. Las ortesis´ activas o exoesquele- tos de asistencia a la marcha humana son dispositivos de uso externo para pacientes con problemas de movilidad que aportan la fuerza y movilidad que le falta al usuario. El uso de estos dispositivos puede ser optimo´ utilizado a diario, integrado en el mayor numero´ de activida- des cotidianas posible. Pero las ortesis´ activas comerciales actuales no tienen autonom´ıa suficiente para proporcionar la potencia consumida durante toda una jornada. Las bater´ıas actuales no proporcionan los re- querimientos de potencia que demandan estas ortesis´ activas. Aumen- tar la autonom´ıa energetica´ se ha convertido en uno de los grandes retos para el desarrollo de estos estos dispositivos. En general, el consumo energetico´ de los robots b´ıpedos de uso general es significativamente mayor que el de los humanos u otros b´ıpedos mam´ıferos. A partir de un minucioso analisis´ de la marcha humana y la anatom´ıa de la loco- mocion´ desde el punto de vista energetico´ y basandose´ en el estado del arte de la robotica,´ en esta tesis se propone una estrategia h´ıbrida para reducir el consumo energetico´ en la marcha, primando la aplicabilidad y la fiabilidad para implementarla en el exoesqueleto ATLAS. En el campo de los robots b´ıpedos se distinguen fundamentalmente tres estrategias de eficiencia energetica:´ 1. Optimizar las trayectorias a seguir por el extremo de la pierna para minimizar una funcion´ objetivo relacionada con la energ´ıa consumida. 2. Aprovechar la dinamica´ pasiva (energ´ıa potencial y cinetica)´ de la pierna del robot para realizar el movimiento subactuado o con poca inyeccion´ de energ´ıa. 3. En el diseno˜ de la extremidad robotica,´ modificar su dinamica´ in- cluyendo elementos y mecanismos elasticos´ en las articulaciones para reducir las perdidas´ de energ´ıa en los impactos con el suelo y para acumular y soltar energ´ıa en las fases de la marcha donde el comportamiento energetico´ de las articulaciones sea el mismo que el de un elemento elastico.´ En esta tesis se propone una aproximacion´ h´ıbrida, que trata de aunar los beneficios de cada estrategia anterior. Habitualmente los pacientes objetivo, hacia los que esta´ enfocado el di- seno˜ de estos exoesqueletos, tienen l´ımites articulares importantes, fle- xos de cadera, rodilla y una marcada limitacion´ en el rango de flexion´ en el tobillo. As´ı, la primera estrategia presentada no es directamente aplicable, puesto que la trayectoria del extremo efectivo en las orte-´ sis activas debe calcularse respetando las restricciones anatomicas´ del paciente. La segunda y tercera estrategias planteadas se logran en esta tesis proponiendo e implementado un esquema de control de rigidez en un actuador de rigidez variable (VSA). Gracias a esta estrategia de variacion´ de rigidez se pueden implementar en una misma articulacion´ estrategias de control basadas en la dinami-´ ca pasiva en la marcha, mientras que se puede aportar el par necesario para un control r´ıgido en posicion´ en fases de mayor demanda de par, permitiendo as´ı subactuacion´ en fases de la marcha donde la inercia inherente al movimiento es suficiente para mantenerlo y tambien´ apor- tando el alto par necesario para que la ortesis´ realice movimientos mas´ versatiles´ y no c´ıclicos, como maniobras de sentar y levantar al pa- ciente. A su vez, estableciendo la rigidez adecuada a la articulacion,´ se reduce el consumo en los cambios de direccion´ de la articulacion´ y se puede almacenar y liberar energ´ıa en ciertas fases. Las estrategias de control de la locomocion´ propuestas se han validado a traves´ de su implementacion´ en el prototipo de ortesis´ activa ATLAS. En esta experimentacion´ se refleja la importancia de la variacion´ de rigidez en relacion´ con una marcha eficiente. Esta estrategia h´ıbrida logra una reduccion´ en el consumo energetico´ de 40 %, mientras se mantiene la robustez y fiabilidad de la ortesis´ activa con actuadores r´ıgidos. Los resultados del trabajo de investigacion´ han dado lugar a siete pu- blicaciones en revistas cient´ıficas indexadas y 19 art´ıculos en congre- sos internacionales, varios de los cuales han sido premiados por su excelencia cient´ıfica y tecnica.´ La tesis doctoral ha tenido un impacto relevante en el area´ de la robotica´ de rehabilitacion´ ya que sus resulta- dos estan´ utilizandose´ en entornos reales, dado que los exoesqueletos de marcha pediatricos,´ transferidos a la empresa de base tecnologica´ Marsi Bionics, estan´ siendo utilizados en dos hospitales del pa´ıs en la terapia de enfermedades neuromusculares en la infancia. Acknowledgements I would like to begin by giving thanks the Centre for Automation and Robotics UPM-CSIC in which this thesis was carried out. I also wish to thank my research adviser, Dr. Elena Garcia for her dir- ection, suggestions, patience, advice and the opportunity and privilege of working in this project. My gratitude also extends to my coworkers (Juan Carlos, Manuel, Xavi, Luis, Leonel, Mariano, etc.) for their dedication, advises, help and good moments that we have labored together in the past years on common work.