A hybrid walking neuroprosthesis that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton 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 of lowering power consumption and reducing actuator size for 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, to maintain stability and control performance when disparate dynamics of FES and electric motor are combined, dynamical disturbances such as electromechanical delay (EMD) and muscle fatigue must be considered during the control design process.
We have developed a general framework to coordinate FES of multiple gait-governing muscles with electric motors is presented. A muscle synergy-inspired control framework is used and is motivated mainly to address the actuator redundancy issue. The synergies between FES of the muscles and the electric motors are artificially generated through optimizations. 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.