Variable Cadence Walking and Ground Adaptive Standing With a Powered Ankle Prosthesis

Amanda H. Shultz, Brian E. Lawson, Michael Goldfarb
2016 IEEE transactions on neural systems and rehabilitation engineering  
This paper describes a control approach that provides walking and standing functionality for a powered ankle prosthesis, and demonstrates the efficacy of the approach in experiments in which a unilateral transtibial amputee subject walks with the prosthesis at variable cadences, and stands on various slopes. Both controllers incorporate a finite-state structure that emulates healthy ankle joint behavior via a series of piecewise passive impedance functions. The walking controller incorporates
more » ... algorithm to modify impedance parameters based on estimated cadence, while the standing controller incorporates an algorithm to modulate the ankle equilibrium angle in order to adapt to the ground slope and user posture, and the supervisory controller selects between the walking and standing controllers. The system is shown to reproduce several essential biomechanical features of the healthy joint during walking, particularly relative to a passive prosthesis, and is shown to adapt to variable cadences. The system is also shown to adapt to slopes over a range of ± 15 deg and to provide support to the user in a manner that is biomimetic, as validated by quasi-static stiffness measurements recorded by the prosthesis. Data from standing trials indicate that the user places more weight on the powered prosthesis than on his passive prosthesis when standing on sloped surfaces, particularly at angles of 10 deg or greater. The authors also demonstrated that the prosthesis typically began providing support within 1 s of initial contact with the ground. Further, the supervisory controller was shown to be effective in switching between walking and standing, as well as in determining ground slope just prior to the transition from the standing controller to the walking controller, where the estimated ground slope was within 1.25 deg of the actual ground slope for all trials. Index Terms Powered Prosthesis; Transtibial; Robotics Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/ publications/rights/index.html for more information. Supplemental Material A video has been included which shows the amputee subject walking with the powered prosthesis at three cadences, standing on various slopes, and transitioning between walking and standing.
doi:10.1109/tnsre.2015.2428196 pmid:25955789 pmcid:PMC4627943 fatcat:oox7neksizhuzefyu7hqaulea4