Nonlinear Control of Uncertain Fatigued Human Skeletal Muscle: Theory and Experiments

Rehabilitation through neuromuscular electrical stimulation (NMES) (also called functional electrical stimulation (FES) for specific functional tasks) is applied as a treatment to improve the activities of daily living for some physically impaired individuals. To more rapidly return affected individuals to activities of daily living (and thereby reducing secondary complications and healthcare costs), methods are sought to increase the intensity and duration of rehabilitative treatments. Yet, a fundamental barrier to NMES/FES treatments is the rapid onset of muscle fatigue during repeated contractions. Fatigue yields a decreased muscle force and an increased electromechanical delay between electrical excitation and tension development in a muscle. These effects are known to cause degraded performance and instability during NMES. Compensating for these effects is complicated by the unknown nonlinear muscle force-length and muscle force-velocity relationships. This presentation will detail the development and stability analysis of a NMES controller that accounts for the uncertain and delayed muscle response. The results are obtained through the development of a novel predictor-type method based on Lyapunov-Krasovskii functionals. Experiments on healthy normal volunteers illustrate the performance and robustness of the developed controller.
Warren Dixon received his Ph.D. in 2000 from the Department of Electrical and Computer Engineering from Clemson University. After completing his doctoral studies he was selected as an Eugene P. Wigner Fellow at Oak Ridge National Laboratory (ORNL) where he worked in the Robotics and Energetic Systems Group. In 2004, Dr. Dixon joined the faculty of the University of Florida in the Mechanical and Aerospace Engineering Department. Dr. Dixon’s main research interest has been the development and application of Lyapunov-based control techniques for uncertain nonlinear systems. He has published 3 books, an edited collection, 6 chapters, and over 200 refereed journal and conference papers. His work has been recognized by the 2009 American Automatic Control Council (AACC) O. Hugo Schuck Award, 2006 IEEE Robotics and Automation Society (RAS) Early Academic Career Award, an NSF CAREER Award (2006-2011), 2004 DOE Outstanding Mentor Award, and the 2001 ORNL Early Career Award for Engineering Achievement. Dr. Dixon is a senior member of IEEE. He serves on several IEEE CSS and ASME technical committees, is a member of numerous conference program and organizing committees, and serves on the conference editorial board for the IEEE CSS and RAS and the ASME DSC. He served as an appointed member to the IEEE CSS Board of Governors for 2008. He is currently an associate editor for ASME Journal of Journal of Dynamic Systems, Measurement and Control, Automatica, IEEE Transactions on Systems Man and Cybernetics: Part B Cybernetics, International Journal of Robust and Nonlinear Control, and Journal of Robotics.