Virtual constraint control of a powered prosthetic leg: From simulation to experiments with transfemoral amputees

Robert D. Gregg*, Tommaso Lenzi, Levi J. Hargrove, Jonathon W. Sensinger

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

175 Scopus citations


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 which virtual constraints define 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 called effective shape into 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.

Original languageEnglish (US)
Article number2361937
Pages (from-to)1455-1471
Number of pages17
JournalIEEE Transactions on Robotics
Issue number6
StatePublished - Dec 1 2014


  • Legged locomotion
  • Prosthetics
  • Rehabilitation robotics
  • Robot control
  • Virtual constraints

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Control and Systems Engineering
  • Computer Science Applications


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