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A Control Scheme That Uses Dynamic Postural Synergies to Coordinate a Hybrid Walking Neuroprosthesis: Theory and Experiments

Alibeji, Naji A. and Molazadeh, Vahidreza and Dicianno, Brad E. and Sharma, Nitin (2018) A Control Scheme That Uses Dynamic Postural Synergies to Coordinate a Hybrid Walking Neuroprosthesis: Theory and Experiments. Frontiers in Neuroscience, 12. ISSN 1662-453X

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A hybrid walking neuroprosthesis that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton can be used to restore walking in persons with paraplegia. It provides therapeutic benefits of FES and torque reliability of the powered exoskeleton. Moreover, by harnessing metabolic power of muscles via FES, the hybrid combination has a potential to lower power consumption and reduce actuator size in the powered exoskeleton. Its control design, however, must overcome the challenges of actuator redundancy due to the combined use of FES and electric motor. Further, dynamic disturbances such as electromechanical delay (EMD) and muscle fatigue must be considered during the control design process. This ensures stability and control performance despite disparate dynamics of FES and electric motor. In this paper, a general framework to coordinate FES of multiple gait-governing muscles with electric motors is presented. A muscle synergy-inspired control framework is used to derive the controller and is motivated mainly to address the actuator redundancy issue. Dynamic postural synergies between FES of the muscles and the electric motors were artificially generated through optimizations and result in key dynamic postures when activated. These synergies were used in the feedforward path of the control system. A dynamic surface control technique, modified with a delay compensation term, is used as the feedback controller to address model uncertainty, the cascaded muscle activation dynamics, and EMD. To address muscle fatigue, the stimulation levels in the feedforward path were gradually increased based on a model-based fatigue estimate. A Lyapunov-based stability approach was used to derive the controller and guarantee its stability. The synergy-based controller was demonstrated experimentally on an able-bodied subject and person with an incomplete spinal cord injury.


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Alibeji, Naji A.
Dicianno, Brad
Sharma, Nitin
Date: 10 April 2018
Date Type: Publication
Journal or Publication Title: Frontiers in Neuroscience
Volume: 12
Publisher: Frontiers Media S.A.
DOI or Unique Handle: 10.3389/fnins.2018.00159
Schools and Programs: Swanson School of Engineering > Mechanical Engineering and Materials Science
Refereed: Yes
ISSN: 1662-453X
Official URL:
Article Type: Research Article
Date Deposited: 19 Jun 2020 13:42
Last Modified: 19 Jun 2020 13:42


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