The Development of Hybrid Volitional Control for Robotic Transtibial Prostheses

This dissertation contributes fundamental advances to the control of robotic transtibial prostheses by developing and assessing hybrid volitional control (HVC), a novel modular control framework. HVC is designed to enable reliable autonomous control for standard cyclic tasks, as well as direct user control to alter or augment the behavior of the prosthetic ankle and achieve non-standard tasks at the user’s discretion. In this dissertation, HVC is investigated through three primary pursuits. Firstly, a framework for HVC applied across the full gait cycle is presented for robotic ankle control, and its implementation is demonstrated by combining finite-state machine (FSM) impedance control with direct myoelectric control (DMC). The utility of HVC is shown, in that it allows users to walk on level ground with biomechanics similar to able-bodied individuals, as well as to volitionally stand on tip-toes, tap the foot, side step, walk backwards, and kick. Secondly, different volitional calibration postures and their relationships with volitional control performance are investigated to fill the need for calibration standardization within HVC and all myoelectric control approaches. Fundamental calibration differences due to lower-limb muscular physiology of individuals with and without amputation are uncovered, and myoelectric calibration recommendations are made. Thirdly, a novel continuous phase variable impedance control approach based on the global tibia kinematics is used to ultimately improve the performance of HVC. This HVC implementation enables seamless transition to other cyclic tasks, such as ramp ascent and descent, by volitionally adapting the controller without requiring task classification or additional controller tuning. User feedback throughout this work shows that HVC is more useful and produces higher overall satisfaction compared to various autonomous controllers. Effectively incorporating the volitional input of the user with reliable autonomous control via HVC offers a pathway to further improve the mobility, independence, and quality of life of individuals with amputation.