Abstract
This paper presents a potential solution to the challenge of configuring powered knee-ankle prostheses in a clinical setting. Typically, powered prostheses use impedance-based control schemes that contain several independent controllers which correspond to consecutive periods along the gait cycle. This control strategy has numerous control parameters and switching rules that are generally tuned by researchers or technicians and not by a certified prosthetist. We propose an intuitive clinician control interface (CCI) in which clinicians tune a powered knee-ankle prosthesis based on a virtual constraint control scheme, which tracks desired periodic joint trajectories based on a continuous measurement of the phase (or progression) of gait. The interface derives virtual constraints from clinician-designed joint kinematic trajectories. An experiment was conducted in which a certified prosthetist used the control interface to configure a powered knee-ankle prosthesis for a transfemoral amputee subject during level-ground walking trials. While it usually takes engineers hours of tuning individual parameters by trial and error, the CCI allowed the clinician to tune the powered prosthesis controller in under 10 min. This allowed the clinician to improve several amputee gait outcome metrics, such as gait symmetry. These results suggest that the CCI can improve the clinical viability of emerging powered knee-ankle prostheses.
Highlights
Persons living with limb loss above the knee generally use mechanically passive prostheses that dissipate energy instead of actively inputting energy to replicate normative biomechanics [1], [2]
We propose an intuitive clinician control interface (CCI) as a tuning tool that leverages this clinical expertise to adjust the prosthetic joint kinematics, which are converted into virtual constraints using the methods of Quintero et al [25] and Rezazadeh et al [26] for control of the powered knee-ankle prosthesis
This paper presents the design of the CCI tool in the context of the virtual constraint control system, which was used by a certified prosthetist to quickly and effectively tune a powered knee-ankle prosthesis for an amputee subject
Summary
Persons living with limb loss above the knee generally use mechanically passive prostheses that dissipate energy instead of actively inputting energy to replicate normative biomechanics [1], [2]. They consist of a heuristic rule-based control scheme, such as a finite state machine, that contains a different controller for each portion of the divided gait cycle [8]–[10], [13], [14] These controllers typically emulate joint stiffness and damping (i.e., impedance), which tend to change across users and tasks. This presents a challenging tuning problem for powered knee-ankle prostheses, which have dozens of impedance parameters and switching rules that must be tuned by a technical expert (usually an engineer) who is very familiar with the effect of each parameter on the control system and the user’s response. This technical process can take several hours for each user [15], [16], which is one of the major reasons that powered knee-ankle prostheses have not been commercialized for clinical use
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