Shared Control of Functional Electrical Stimulation and an Electric Motor in a Hybrid Neuroprosthesis
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Functional Electrical Stimulation (FES) can be used to artificially activate paralyzed lower limb muscles to restore walking and standing function in persons with neurological disorders. Despite its potential, FES-based walking neuroprosthesis has achieved limited acceptability among persons with paraplegia. This low acceptance is primarily due to the early onset of muscle fatigue during FES and difficulty in obtaining a consistent and reliable response from the paralyzed muscle using traditional control methods. We are employing a hybrid strategy that integrates FES with a powered exoskeleton to overcome these hurdles. This hybrid strategy has several advantages. The main advantage is that the effects of muscle fatigue and any inconsistent response from FES can be compensated by the active exoskeleton, which can potentially lead to improved functional mobility in users with neurological impairments. Other advantages include a reduction in the overall weight of the exoskeleton and neuroplastic improvements in the neuromuscular system due to FES. However, closed-loop control methods are required to effectively integrate FES with a powered exoskeleton because the hybrid combination leads to redundancy in actuation and needs criteria to allocate control between FES and an electric motor. I will present algorithms and models recently developed by our research group to control the hybrid exoskeleton. These methods include: 1) a muscle fatigue model to inform the onset of muscle fatigue and muscle recovery during FES, 2) Shared control of FES and electric motor based on the fatigue model, and 3) muscle synergy inspired control of a hybrid walking exoskeleton.
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