Journal
CONTROL ENGINEERING PRACTICE
Volume 59, Issue -, Pages 204-219Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.conengprac.2016.07.015
Keywords
Functional electrical stimulation; Muscle fatigue; Dynamic surface control; Synergies; Human inspired control; Adaptive control; State estimator; Input delays; Electromechanical delays
Funding
- National Science Foundation [1462876]
- University of Pittsburgh's Competitive Medical Research Fund
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1462876] Funding Source: National Science Foundation
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To restore walking and standing function in persons with paraplegia, a hybrid walking neuroprosthesis that combines a powered exoskeleton and functional electrical stimulation (FES) can be more advantageous than sole FES or powered exoskeleton technologies. However, the hybrid actuation structure introduces certain control challenges: actuator redundancy, cascaded muscle activation dynamics, FES-induced muscle fatigue, and unmeasurable states. In this paper, a human motor control inspired control scheme is combined with a dynamic surface control method to overcome these challenges. The new controller has an adaptive muscle synergy-based feedforward component which requires a fewer number of control signals to actuate multiple effectors in a hybrid neuroprosthesis. In addition, the feedforward component has an inverse fatigue signal to counteract the effects of the muscle fatigue. A dynamic surface control (DSC) method is used to deal with the cascaded actuation dynamics without the need for acceleration signals. The DSC structure was modified with a delay compensation term to deal with the electromechanical delays due to FES. A model based estimator is used to estimate the unmeasurable fatigue and actuator activation signals. The development of the controller and a Lyapunov stability analysis, which yielded semi-global uniformly ultimately boundedness, are presented in the paper. Computer simulations were performed to test the new controller on a 2 degrees of freedom fixed hip model after which preliminary experiments were conducted on one able-bodied male subject in the fixed hip configuration. (c) 2016 Elsevier Ltd. All rights reserved.
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