title: Virtual Constraint Control of a Powered Prosthetic Leg: From Simulation to Experiments with Transfemoral Amputees.
abstract: Recent powered (or robotic) prosthetic legs independently control different joints and time periods of the gait cycle, resulting in control parameters and switching rules that can be difficult to tune by clinicians. This challenge might be addressed by a unifying control model used by recent bipedal robots, in whichvirtual constraintsdefine joint patterns as functions of a monotonic variable that continuously represents the gait cycle phase. In the first application of virtual constraints to amputee locomotion, this paper derives exact and approximate control laws for a partial feedback linearization to enforce virtual constraints on a prosthetic leg. We then encode a human-inspired invariance property calledeffective shapeinto virtual constraints for the stance period. After simulating the robustness of the partial feedback linearization to clinically meaningful conditions, we experimentally implement this control strategy on a powered transfemoral leg. We report the results of three amputee subjects walking overground and at variable cadences on a treadmill, demonstrating the clinical viability of this novel control approach.
authors.affiliation: Departments of Bioengineering and Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080 USA.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Gregg
authors.affiliation: Center for Bionic Medicine, Rehabilitation Institute of Chicago and the Department of Physical Medicine & Rehabilitation, Northwestern University, Chicago, IL 60611 USA.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Lenzi
authors.affiliation: Center for Bionic Medicine, Rehabilitation Institute of Chicago and the Department of Physical Medicine & Rehabilitation, Northwestern University, Chicago, IL 60611 USA.
authors.forename: Levi J
authors.initials: LJ
authors.lastname: Hargrove
authors.affiliation: Institute of Biomedical Engineering and Department of Electrical and Computer Engineering, University of New Brunswick, Fredericton, NB E3B 9P8, Canada.
authors.forename: Jonathon W
authors.initials: JW
authors.lastname: Sensinger