Master of Engineering, Case Western Reserve University, 2022, EMC - Mechanical Engineering

This thesis details the research, design, manufacturing, and testing of an ab/adduction power unit to be used on a lower extremity hybrid neuroprosthesis (HNP) for individuals with paralysis due to spinal cord injuries. The device is intended to actuate the hip in ab/adduction for better stability and a more natural gait. The power unit is comprised of a brushless motor, two stages of compound spur gears, followed by a single planetary stage, as well as torque and position sensors. This unit builds on previous designs but differs significantly in its torque and speed requirements. Peak torque is required for up to 40% of the gait cycle, requiring more gearing (146:1) than previous power units. After bench testing, the unit was found to have a breakaway torque of 2.65-3.17 N - m, a peak torque of 65 N - m at 6.45-7.17A, and maximum speed of 137 ◦/s. It weighs 2.56 kg and has an isometric efficiency of 87% - 97.1%.

Committee: Roger Quinn (Committee Chair); Musa Audu (Committee Member); Ronald Triolo (Committee Member) Subjects: Biomechanics; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2016, Biomedical Engineering

Stepping can be restored in individuals with paraplegia due to spinal cord injury (SCI) with a hybrid neuroprosthesis (HNP) that combines functional neuromuscular stimulation (FNS) and passive controllable lower-limb bracing. FNS applies small electrical pulses to peripheral motor nerves, thereby contracting the paralyzed muscles and generating joint torques capable of mobilizing the limb for stepping. Passive controllable lower-limb bracing can be designed to lock, unlock, or couple joints to provide support and stability. Prior work showed that the HNP enabled individuals with motor complete thoracic SCI to stand, walk, and negotiate stairs. However, knee flexion during pre-swing phase of gait can be inadequate and result in inconsistent foot-floor clearance, increasing the risk of tripping or falling. The stand-to-sit (STS) transition was also poorly controlled and resulted in high impact with the seating surface. Therefore, we hypothesized that a HNP with context-dependent hydraulic hip-knee coupling (HKC) would more effectively normalize STS maneuvers and restore pre-swing phase knee flexion during walking in individuals with paraplegia than stimulation alone. Novel kinematic HKC and kinetic knee damping hydraulic mechanisms were incorporated into the HNP to control the knee during STS transitions. By imposing simple coupling or damping constraints, individuals with SCI completed the STS with improved coordination between hip and knee joint angles, lowered knee angular velocities, decreased upper limb forces by 70%, and reduced impact forces by half when compared to sitting with stimulation alone. To achieve sufficient foot-floor clearance by assisting pre-swing knee flexion during gait, a kinematic HKC hydraulic mechanism and kinetic elastomer spring were evaluated. The hydraulic coupling mechanism had high passive resistances, making the system impractical during gait. Future work may evaluate alternative HKC methods. The elastomer spring successfully (open full item for complete abstract)

Committee: Dominique Durand Ph.D. (Committee Chair); Ronald Triolo Ph.D. (Advisor); Malcolm Cooke Ph.D. (Committee Member); Patrick Crago Ph.D. (Committee Member); Musa Audu Ph.D. (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Robotics

Doctor of Philosophy, Case Western Reserve University, 2012, Biomedical Engineering

A hybrid neuroprosthesis combines functional neuromuscular stimulation with controllable bracing to restore walking function after paralysis from spinal cord injury. This approach confines stimulation to driving the limbs forward while utilizing bracing to lock joints for postural support during stance. However, a stiff leg during stance is inefficient and can limit the range of achievable walking tasks. We hypothesize that a hybrid neuroprosthesis which regulates joint motion under loading will augment stimulation driven gait to create better walking performance. A novel variable impedance mechanism was developed to control the knee joint during stance phase of locomotion. This mechanism was optimized to provide adequate torque for regulation of knee motion under load at all joint angles, creating an orthosis capable of achieving power absorption which is not possible through stimulation of muscles or lockable orthotics. A finite state, closed loop control system based on sensor feedback was developed to coordinate activation of the variable impedance knee mechanism with electrical stimulation to create a new hybrid neuroprosthesis for walking (VIKM-HNP). The goal of the VIKM-HNP was to allow knee extensor muscles to rest while providing power absorption for stance phase knee flexion and enabling unencumbered swing phase motion. The new VIKM-HNP was evaluated during level walking in two individuals with thoracic level spinal cord injury. The results showed a significant increase in stance knee flexion and power absorption while reducing knee extensor stimulation duty cycle by up to 40%. The altered knee behavior created more steady forward progression, increased minimum instantaneous gait speed, and reduced impulsive ground reaction forces compared to stimulation alone. A second finite state machine was developed to enable step-by-step forward stair descent using the VIKM-HNP. Knee extensor stimulation of the trailing limb was deactivated while the orthosis was a (open full item for complete abstract)

Committee: Melissa Knothe Tate PhD (Committee Chair); Ronald Triolo PhD (Advisor); Robert Kirsch PhD (Committee Member); Roger Quinn PhD (Committee Member); Musa Audu PhD (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Robotics

Doctor of Philosophy, Case Western Reserve University, 2010, Biomedical Engineering

A hybrid neuroprosthesis (HNP) was developed with the goal of providing improved gait to individuals with paraplegia relative to existing assistive gait systems. The HNP is an approach to restoring gait by combining a lower extremity exoskeleton with functional neuromuscular stimulation (FNS). Individually, exoskeletons apply constraints for support, but provide limited step length and depend on upper extremity actions on a walker for forward propulsion. Conversely, FNS mobilizes the limbs through electrical pulses to paralyzed muscles. However, muscles targeted for stimulation quickly fatigue and provide inadequate postural support. The HNP was designed to functionally combine the supportive features of the exoskeleton and joint mobility of FNS. Controllable knee and hip joint mechanisms were developed to support the user while allowing for functional motion from FNS for forward progression. These mechanisms were optimized for maximal torque when supporting a joint and minimal resistance when driven by FNS. A closed-loop controller based on sensor measurements of joint dynamics was developed to synchronize exoskeletal operation with muscle stimulus activity. The objectives were to modulate joint constraints to provide continual support to the user while minimizing the deleterious effects of the constraints on joint mobility, deactivate stimulus to target muscles when certain exoskeletal constraints are engaged to allow the target muscles to rest, and modulate FNS from baseline levels to achieve functional joint positions. The operational response of the controller and mechanisms were characterized through simulation, bench, and able-bodied testing. Implementation of the HNP with an individual with paraplegia respectively showed a 40 % and 16 % reduction in maximum exerted upper extremity forces relative to exoskeleton-only and FNS-only gait. Step lengths were shown to be comparable between HNP and FNS-only gait. When comparing the HNP with and without the FNS modu (open full item for complete abstract)

Committee: Robert Kirsch PhD (Committee Chair); Ronald Triolo PhD (Committee Member); Roger Quinn PhD (Committee Member); Patrick Crago PhD (Committee Member); Musa Audu PhD (Advisor) Subjects: Biomedical Research; Design; Engineering; Health Care; Mechanical Engineering; Rehabilitation; Technology