Development of control stategies for a variable stiffness ankle exoskeleton for gait rehabilitation

Abstract

Currently, designing robotic devices to assist and rehabilitate the ankle is challenging due to the joint's complexity and its fundamental role in walking. This research field has been motivated by the disability's high incidence of neurological disorders and their effects in Activities of Daily Living's (ADL) execution that reduces people's life quality. This way, powered ankle-foot orthoses (PAFOs) or ankle exoskeletons are being developed to counteract the gait limitation and to improve motor recovery. In this context, this master's dissertation presents the design, development, and implementation of a novel wearable and portable ankle exoskeleton, called T-FLEX, based on Variable Stiffness Actuators (VSAs). Thus, different high-level control strategies were developed and implemented to support gait rehabilitation with T-FLEX. Likewise, an experimental characterization determined the T-FLEX's applicability in assistive scenarios and measured the device's capabilities during this task. Lastly, two experimental validations with people who exhibited ankle dysfunctions were carried out to assess the device's effectiveness during gait rehabilitation. In general terms, this dissertation determined that T-FLEX is capable of assisting gait patterns with gait cycle duration greater than 0.74 seconds. Moreover, this work assessed the T-FLEX's actuation system in a passive orthotic structure during a first-use trial and evaluated T-FLEX in a rehabilitation program with a chronic stroke patient. The gait assistance assessment showed improvements in foot clearance and lower limb's kinematics. However, the users exhibited reductions in Spatio-temporal parameters related mainly to the orthotic structure used in this study. For the validation in therapy mode, T-FLEX evidenced positive effects: (1) increasing cadence, (2) reducing the plantarflexion movement during swing phase, (3) decreasing the spasticity level and increasing the passive lower limb joints' range of motion (ROM) after 18 sessions. T-FLEX can assist human gait and support rehabilitation processes of neurological patients with ankle dysfunctions. Future works will address improvements in the device synchronization, the assessment in a larger sample population, the interactive feedback strategies' development, and the dynamic experimental characterization' execution.