Phase Variable Impedance Hybrid Volitional Control for Transtibial Prostheses

Extending transtibial prostheses control beyond level walking is key to enabling activities of daily living and improving quality of life for individuals with amputation. Phase variable impedance hybrid volitional control (PVI-HVC) combines the reliability of autonomous control with the freedom and embodiment of volitional control. PVI-HVC and the first phase variable impedance controller (PVIC) based on global tibia kinematics are compared to a finite-state machine (FSM) impedance controler and FSM-HVC for three individuals with transtibial amputations walking on a level treadmill and an overground ramp. By incorporating residual muscle activation, PVI-HVC allowed volitional adaptation to activities including level walking, ramp ascent/descent, and tiptoe standing, without activity classification or controller changes. Compared to FSM-HVC, PVI-HVC produced smoother kinematics and kinetics, more closely resembling healthy biomechanics. FSM-HVC showed sensitivity to inter-subject variability, particularly in state transitions, and undesirable interactions between autonomous and volitional control contributions not present with PVI-HVC. All subjects rated PVI-HVC the highest in overall satisfaction and better than or equal to FSM-HVC in usefulness, ease of use, reliability, and comfort. PVI-HVC is a promising solution for seamlessly extending control to a wide range of activities.