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Abstract

Assistive robot technologies are devices such as exoskeletons and prostheses that provide
movement assistance, support, can augment users or even replace their limbs. Currently
commercially available devices have limited performance and power capacity, and are expensive.
The focus of this thesis is on the integration and use of compliant actuation
technologies that combine motors and passive elastic elements to enable superior performance
of exoskeleton devices. Their integration can resolve the above-listed issues with
features like mechanical adaptivity, energy efficiency, increased safety and reduced costs.
The thesis revolves around their integration and is divided into three parts.
In the first part, a quasi-passive ankle exoskeleton is evaluated. The exoskeleton features
a passive elastic element and clutch assembly that is placed in parallel to the human
calf muscles. Through correct clutch activation timing and proper stiffness of the elastic
element, the strain on the calf muscles is reduced without the use of heavy motors, resulting
in easier walking. The prototype and its effects are evaluated through two pilot
studies and analysed. One study assesses its physiological effect through measurements
of oxygen consumption, EMG muscle activity and hearth-rate and the other assesses the
user's subjective perception of the exoskeleton use with a questionnaire.
Part two shows the development of a novel, more efficient way of stiffness variation
that could be used to replace the process of manual spring exchange in the passive ankle
exoskeleton. The new principle combines characteristics of a cam mechanism and a
variable lever mechanism. A compact structure, a nearly linear torque-deflection characteristics
and fast, energy-efficient stiffness adaptation are the main properties of the
pseudo-linear variable lever variable stiffness actuator (PLVL-VSA). The research includes
a mathematical model, a fully-functional prototype, an elbow exoskeleton device featuring
the proposed mechanism, extensive evaluation and analysis of the proposed concept, and
finally a technique for parameter optimization of its components.
The third part focuses on the development of a mechanically compliant exoskeleton
device. Integration of mechanical compliance despite its additional weight and complexity
is possible through the use of modular design techniques and by moving all the heavy
components onto the user's back. Bowden cable transmission allows the transfer of power
from the user's back to the exoskeleton joints to retain a light frame with minimal inertia.
This research analyses the power loss and control performance degradation due to Bowden
cable friction and resolves it through mathematical modelling and the use of sensor fusion
methods. The focus lies on the external torque estimation in light of high levels of friction
by combining the signals from an integrated load cell and Bowden cable stretch measurements.
The methods are evaluated on a new upper-limb exoskeleton prototype, which is
at the end prepared for a possible integration with variable stiffness components.