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Abstract

Wearable robotics holds promise for enhancing human capabilities and addressing motor
challenges in individuals with impairments, amputations, or those who are healthy. Exoskeletons,
among various wearable devices, are designed to be worn on the upper or lower
limbs. While some applications, like in the medical field, have been widely adopted, others
still face unique challenges. These challenges primarily center around Actuation, Control,
and Ergonomics. This thesis primarily focuses on inventing actuators with novel superior
functionalities together with corresponding control algorithms and their application in
lower limb exoskeletons. The thesis contains four main parts, each representing a distinct
phase of the research process.
In the first part, a quasi-passive pneumatic variable stiffness mechanism is introduced,
mathematically described, and experimentally evaluated. This mechanism is distinctive as
it utilizes a vacuum to draw air from the atmosphere, thereby adjusting the pressure inside
the actuator. This approach enables the pneumatic mechanism to mimic the behavior of a
nonlinear variable stiffness spring without requiring an external air supply. Additionally,
through a proposed valve combination, the mechanism can be completely deactivated to
allow free motion, while also offering the capability to incrementally adjust stiffness.
In the second part, based on the fundamental principles of the quasi-passive mechanism,
the air harvesting capabilities are extended to the entire Pneumatic Exoskeleton
Joint Mechanism (PEJM). This design introduces additional components, including the
Pneumatic Artificial Muscle (PAM), which acts as a soft reservoir for the harvested air
and additionally influences the stiffness of the joint. At this stage, the exoskeleton joint
remains quasi-passive and continues to rely on vacuum for air intake. The joint undergoes
experimental validation using a setup that does not involve human subjects.
In the third part, a mechatronic concept of a complete pneumatic fully portable bilateral
knee exoskeleton is presented. The novelty lies in its multimodal functionality, allowing
the exoskeleton to operate in both active and quasi-passive modes using the same actuator.
This versatility improves energy efficiency by enabling air recovery in quasi-passive mode
and the reuse of stored air in active mode, which also uses an integrated air pump. A pilot
study involving a single healthy participant is conducted to demonstrate simultaneous
energy recovery and human assistance.
Finally, the fourth part is about the hybrid rigid-soft and pneumatic-electromechanical
exoskeleton for multi-joint lower limb assistance. This concept uses tendon-driven electromechanical
actuation for the hip joint and a pneumatic rigid exoskeleton for the knee
joint. The hip joint, with its three active degrees of freedom (DoF), benefits from tendondriven
actuation, simplifying mechanics. Conversely, the knee joint, with its single active
DoF crucial for weight-bearing, exhibits compliance during the weight acceptance phase,
making it suitable for a pneumatic exoskeleton. The exoskeleton is evaluated in human
studies while measuring their metabolic cost, muscular activity, and kinematics.