BIOMEDICAL ENGINEERING

A HNP combines a lower extremity exoskeleton with the artificial activation of paralyzed muscle by functional neuromuscular stimulation (FNS) to facilitate functional gait in individuals with paraplegia. The objective of this project is to develop a hybrid neuroprosthesis system (HNP) with a novel hip mechanism and sensor-based feedback control system. A variable constraint hip mechanism (VCHM) has been developed to provide postural stability and uninhibited sagittal hip rotation throughout the gait of individuals with paraplegia. The VCHM utilizes a hydraulic system to reciprocally couple the hips or individually lock and/or free a hip to rotate in one or both sagittal directions. The sensor-based feedback controller for the HNP consists of two modules: 1) a finite state machine to modulate the exoskeleton constraints and 2) a fuzzy inference system (FIS) based gait event detector (GED) to modulate FNS patterns for gait corrections and synchronize the FNS with exoskeleton operation. Bench testing of the VCHM showed the feasibility of utilizing a portable hydraulic system in controlling hip joint kinematics. The passive resistive torques of the VCHM against user sagittal hip rotation at hip angular velocities typical of gait does not exceed 10 % of the achievable hip torque generated by FNS of paralyzed muscle. Bench testing and experiments with able-bodied individuals with the VCHM controller showed that the VCHM could reliably prevent forward trunk tilt and allow for uninhibited functional hip motion throughout the entire gait cycle. Sagittal hip angle excursion between the onset of hip flexion during the stance phases of gait and when the VCHM can effectively prevent further hip flexion does not exceed 1o. Preliminary evaluation of the GED has been conducted on able-body individuals walking with the exoskeleton. Future work will focus on the validation of the VCHM and control system as part of a HNP for paraplegic individuals implanted with FNS systems.