Metabolic studies have shown that there is a metabolic cost associated with carrying a load (Griffin et al, 2003). Further studies have shown that by applying forward propulsive forces a person can walk with a reduced metabolic rate (Farley & McMahon, 1992 and Gottschall & Kram, 2003). Previous work on exoskeleton design has not considered the passive dynamics of walking and has focused on fully actuated systems that are inefficient and heavy. In this thesis, an under-actuated exoskeleton is presented that runs parallel to the human leg. The exoskeleton component design is based on the kinematics and kinetics of human walking. The joint components of the exoskeleton in the sagittal plane consist of a force-controllable actuator at the hip, a variable-damper mechanism at the knee and a passive spring at the ankle. A state-machine control strategy is written based on joint angle and ground-exoskeleton force sensing. Positive, non-conservative power is added at the hip during the walking cycle to help propel the mass of the human and payload forward. At the knee, the damper mechanism is turned on at heel strike as the exoskeleton leg is loaded and turned off during terminal stance to allow knee flexion.

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BWSTT has become an accepted standard of care in gait rehabilitation methods. This type of locomotor training has many functional benefits, but the physical labor costs are considerable. To reduce therapist effort and improve the repeatability of locomotor training, three groups have developed commercially available robotic devices for assisted stepping. The purpose of these robotic devices is to augment locomotor rehabilitation by decreasing therapist manual assistance, increasing the amount of stepping practice, while decreasing therapist effort. Current clinical studies have yielded positive and promising results in locomotor rehabilitation inpatients with neurologic impairments of stroke or SCI. The potential benefits from robotic technology are significant for clinical use and research. As further research is conducted, rehabilitation therapists and patient outcomes will be able to contribute to the development of current and future technologies.

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