Exoskeleton-assisted locomotion: design, control and evaluation of wearable robotic devices

Assistive robotic devices such as exoskeletons and prosthetic limbs have great potential as tools for both augmentation and rehabilitation. However, due to the complexity of controlling these devices, especially in unstructured environments where factors such as walking speed and incline can vary rapidly, it is uncommon to see exoskeletons outside of a clinical or research setting. Prostheses, whilst more common, are typically passive, which limits their ability to match the push off forces associated with healthy gait. Motivated by modern techniques for controlling legged robots, this thesis motivates the pursuit of an optimisation-based approach to the control and design of exoskeletons. We identify a number of open problems within the field, namely (1) how to model the dynamic interaction between a human subject and an attached exoskeleton; (2) identifying the appropriate metric or combination of metrics to optimise for in exoskeleton-assisted locomotion; and (3) how to account for changes in human walking style induced by the presence of external assistive forces. This thesis details attempts to solve each of these problems. We present a methodology for expressing human-exoskeleton system models as a combination of musculoskeletal models, exoskeleton inertial parameters and constraint forces. A specific human-exoskeleton model is detailed, along with a range of methods for modelling the interaction forces which occur at the attachment points between the human and exoskeleton agents. Experimental motion data is analysed using musculoskeletal modelling software (OpenSim) to quantify the effect that each of these interaction models, which represent various degrees of approximation, have on the resulting humanexoskeleton dynamics. Applying exoskeleton assistance is inherently a shared control problem. The overall goal is not to achieve a prescribed motion at any cost, or to do so while minimising exoskeleton joint torques, but rather to enhance aspects of the assisted humans motions; for example, increasing energy efficiency or stability. Therefore, in order to optimise exoskeleton control patterns we must first consider what it means for the resultant gait patterns to be optimal, or even good. We present a detailed analysis of exoskeleton-assisted walking in healthy subjects, with a particular focus on identifying those metrics which are invariant to changes in walking condition (e.g. walking speed or incline). We posit that such metrics, which exhibit strong invariance properties, are good candidates for the objective function of an optimisation-based controller. Human walking strategies are unique and complex, and the problem of predicting the effect of exoskeleton assistance on a subjects gait pattern is a challenging one. In recent years, success has been had by methods which aim to learn suitable assistance strategies directly from a subject, via a process known as human-in-the-loop optimisation. We present a novel humanin- the-loop framework which utilises musculoskeletal modelling to make the learning process more time-efficient. Our method is evaluated on a number of subjects walking on a treadmill with exoskeleton assistance. In addition, we also explore how human-in-the-loop optimisation can be used to inform the design of exoskeletons to enhance their assistive capabilities. Overall, these contributions represent a step towards enabling the wider usage of exoskeletons and other assistive robotic devices, which could lead to significant improvements to quality of life for many

Feasibility Analysis of a Powered Lower-Limb Orthotic for the Mobility Impaired User

Powered orthotic devices can be used to restore mobility to the impaired user, and may thereby assist them in daily living tasks. An investigation is performed herein to examine the feasibility of a powered lower-limb orthotic in assisting the sit-to-stand task by 50% of the required torque. Feasibility is considered via simulation. A three-link sit-to-stand model, which is driven by kinematic data, is developed. Models of a Pneumatic Muscle Actuator and a DC motor are used to determine which of the two technologies can make a more appropriate contribution to the sit-to-stand task. Simulation revealed that both the Pneumatic Muscle Actuator and the DC motor are reasonable actuator choices, and neither limited the ability to achieve 50% torque assistance. The ability to assist the task was, however, limited by the ability to derive a control signal for the actuator from the user-orthotic interface. It was concluded that the user-orthotic interface requires further investigation. It was also found that while both actuator technologies are suitable for contributing 50% of the required torque, the Pneumatic Muscle Actuator is preferable due to its ability to scale to greater torques

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

Rehabilitation Engineering

Population ageing has major consequences and implications in all areas of our daily life as well as other important aspects, such as economic growth, savings, investment and consumption, labour markets, pensions, property and care from one generation to another. Additionally, health and related care, family composition and life-style, housing and migration are also affected. Given the rapid increase in the aging of the population and the further increase that is expected in the coming years, an important problem that has to be faced is the corresponding increase in chronic illness, disabilities, and loss of functional independence endemic to the elderly (WHO 2008). For this reason, novel methods of rehabilitation and care management are urgently needed. This book covers many rehabilitation support systems and robots developed for upper limbs, lower limbs as well as visually impaired condition. Other than upper limbs, the lower limb research works are also discussed like motorized foot rest for electric powered wheelchair and standing assistance device