Towards Bidirectional Lower Limb Prostheses: Restoring Proprioception Using EMG Based Vibrotactile Feedback

Abstract

Current lower limb prostheses lack bidirectional communication and the ability to generate power. As a result, they do not effectively replace the lost limb. Electromyography (EMG) control has been widely implemented in upper limb prostheses but is still underdeveloped in lower limb prostheses. The aim of this thesis is to design, develop, and evaluate a novel vibrotactile feedback system in combination with an EMG-controlled powered knee or ankle prosthesis to restore proprioception. This thesis demonstrates that discrete localised vibrations enable proprioceptive sensing for the user through the described sensory feedback system. Three subjects with a major lower limb amputation performed level ground and inclined walking tests under various conditions. The experiments reported in the thesis compare the effects of EMG control with and without sensory feedback on temporal gait symmetry and psychosocial metrics, i.e. cognitive workload assessment, prosthesis embodiment, and confidence. The key results from this thesis are the following: temporal gait symmetry and psychosocial measures tended to improve within and between session, though the results varied widely between subjects. Interference in the rest EMG signal was found when the vibrotactors were activated. Further, subjects were able to distinguish between sensory feedback levels. EMG control initially reduced gait symmetry, but gait symmetry was later increased with sensory feedback. Higher symmetry scores were measured after sensory feedback was turned off, demonstrating learning retention. Similar trends were measured in psychosocial metrics, indicating that the sensory feedback system contributed to perceived improvements of the prosthesis. In summary, results show promising effects of using vibrotactile feedback in combination with EMG control in lower limb prostheses, despite the need to improve system robustness. Longer training with EMG and sensory feedback might improve quality of life of prosthesis users even more