Continuous-Phase Control of a Powered Knee-Ankle Prosthesis: Amputee Experiments Across Speeds and Inclines

David Quintero, Dario J. Villarreal, Daniel J. Lambert, Susan Kapp, Robert D. Gregg

Research output: Contribution to journalArticlepeer-review

146 Scopus citations


Control systems for powered prosthetic legs typically divide the gait cycle into several periods with distinct controllers, resulting in dozens of control parameters that must be tuned across users and activities. To address this challenge, this paper presents a control approach that unifies the gait cycle of a powered knee-ankle prosthesis using a continuous, user-synchronized sense of phase. Virtual constraints characterize the desired periodic joint trajectories as functions of a phase variable across the entire stride. The phase variable is computed from residual thigh motion, giving the amputee control over the timing of the prosthetic joint patterns. This continuous sense of phase enabled three transfemoral amputee subjects to walk at speeds from 0.67 to 1.21 m/s and slopes from -2.5° to +9.0°. Virtual constraints based on task-specific kinematics facilitated normative adjustments in joint work across walking speeds. A fixed set of control gains generalized across these activities and users, which minimized the configuration time of the prosthesis.

Original languageEnglish (US)
Pages (from-to)686-701
Number of pages16
JournalIEEE Transactions on Robotics
Issue number3
StatePublished - Jun 2018
Externally publishedYes


  • Legged locomotion
  • prosthetics
  • rehabilitation robotics
  • robot control
  • virtual constraints

ASJC Scopus subject areas

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


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