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First steps toward translating robotic walking to prostheses: a nonlinear optimization based control approach

Abstract

This paper presents the first steps toward successfully translating nonlinear real-time optimization based controllers from bipedal walking robots to a self-contained powered transfemoral prosthesis: AMPRO, with the goal of improving both the tracking performance and the energy efficiency of prostheses control. To achieve this goal, a novel optimization-based optimal control strategy combining control Lyapunov function based quadratic programs with impedance control is proposed. This optimization-based optimal controller is first verified on a human-like bipedal robot platform, AMBER. The results indicate improved (compared to variable impedance control) tracking performance, stability and robustness to unknown disturbances. To translate this complete methodology to a prosthetic device with an amputee, we begin by collecting reference locomotion data from a healthy subject via inertial measurement units (IMUs). This data forms the basis for an optimization problem that generates virtual constraints, i.e., parameterized trajectories, specifically for the amputee . A online optimization based controller is utilized to optimally track the resulting desired trajectories. An autonomous, state based parameterization of the trajectories is implemented through a combination of on-board sensing coupled with IMU data, thereby linking the gait progression with the actions of the user. Importantly, the proposed control law displays remarkable tracking and improved energy efficiency, outperforming PD and impedance control strategies. This is demonstrated experimentally on the prosthesis AMPRO through the implementation of a holistic sensing, algorithm and control framework, resulting in dynamic and stable prosthetic walking with a transfemoral amputee.

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Acknowledgments

This research is supported under: NSF CAREER Award CN-S-0953823 and Texas Emerging Technology Fund 11062013. This research has approval from the Institutional Review Board from Texas A&M University with IRB2014-0382F for testing with human subjects.

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Correspondence to Huihua Zhao.

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This is one of several papers published in Autonomous Robots comprising the “Special Issue on Assistive and Rehabilitation Robotics”.

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Zhao, H., Horn, J., Reher, J. et al. First steps toward translating robotic walking to prostheses: a nonlinear optimization based control approach. Auton Robot 41, 725–742 (2017). https://doi.org/10.1007/s10514-016-9565-1

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  • DOI: https://doi.org/10.1007/s10514-016-9565-1

Keywords

  • Transfemoral prosthesis control
  • Real-time optimal control
  • Hybrid systems
  • Quadratic program
  • Optimization problem