A Phase Variable Approach for Improved Rhythmic and Non-Rhythmic Control of a Powered Knee-Ankle Prosthesis.

Siavash Rezazadeh,Emma Reznick,Leslie Gray,Nikhil Divekar,Robert D. Gregg,David Quintero

doi:10.1109/access.2019.2933614

Abstract

Although there has been recent progress in control of multi-joint prosthetic legs for rhythmic tasks such as walking, control of these systems for non-rhythmic motions and general real-world maneuvers is still an open problem. In this article, we develop a new controller that is capable of both rhythmic (constant-speed) walking, transitions between speeds and/or tasks, and some common volitional leg motions. We introduce a new piecewise holonomic phase variable, which, through a finite state machine, forms the basis of our controller. The phase variable is constructed by measuring the thigh angle, and the transitions in the finite state machine are formulated through sensing foot contact along with attributes of a nominal reference gait trajectory. The controller was implemented on a powered knee-ankle prosthesis and tested with a transfemoral amputee subject, who successfully performed a wide range of rhythmic and non-rhythmic tasks, including slow and fast walking, quick start and stop, backward walking, walking over obstacles, and kicking a soccer ball. Use of the powered leg resulted in clinically significant reductions in amputee compensations for rhythmic tasks (including vaulting and hip circumduction) when compared to use of the take-home passive leg. In addition, considerable improvements were also observed in the performance for non-rhythmic tasks. The proposed approach is expected to provide a better understanding of rhythmic and non-rhythmic motions in a unified framework, which in turn can lead to more reliable control of multi-joint prostheses for a wider range of real-world tasks.

Highlights

The vast majority of lower-limb amputees use mechanically passive prosthetic legs, which can only dissipate energy during locomotion
The main goal of this work was to demonstrate the ability of the controller to facilitate both rhythmic tasks as well as a range of non-rhythmic tasks and the improvements compared to the amputee subject’s passive leg
A new control framework for a range of rhythmic and nonrhythmic tasks was designed for powered knee-ankle prostheses and validated through experiments with an above-knee amputee subject

Summary

Introduction

The vast majority of lower-limb amputees use mechanically passive prosthetic legs, which can only dissipate energy during locomotion. This limits the ability of amputees to efficiently perform various ambulation modes, walking at variable speeds or slopes. The human gait cycle can be divided into different phases (namely, stance and swing phase) and sub-phases (for example, weight acceptance, push-off, early swing, etc.), each serving a specific purpose in locomotion [8] This perspective was preserved in control design for powered lower-limb prostheses, which involves first detecting the correct sub-phase and controlling that particular behavior of the prosthetic joints [5], [9]–[12].

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