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There are over 270,000 people in the United States suffering from spinal cord injury. Currently, the wheelchair is the most commonly prescribed mobility solution for these individuals. Unfortunately, numerous health problems can be developed as a side effect of extended sitting. Studies have indicated that standing and walking for wheelchair bound individuals can improve overall health and mitigate these secondary health risks. Several passive walking devices exist, however these approaches are impractical due to the high metabolic cost associated with walking. Powered lower extremity exoskeletons have the capacity to substantially improve overall health and mobility of paralyzed individuals. The practicality of previous mobile medical exoskeletons has been limited due to cumbersome walking dynamics, high system mass and high cost. This work introduces the Steven Exoskeleton, a lightweight minimally actuated assistive exoskeleton developed as a device that can be intuitively adopted by manual wheelchair users. This device builds off of the successes of several generations of low cost medical exoskeletons developed at the UC Berkeley Robotics and Human Engineering Laboratory. Several elements of exoskeleton gait have been refined for the Steven Exoskeleton allowing better control of walking speed with more fluid walking dynamics. By smoothing hip trajectories and increasing stride length it has been possible to increase overall speed and pilot comfort. New hardware allows tunable hip and spine flexibility, improving pilot performance and adaptability. Through hardware and control refinement, comfortable walking speed has been increased to 0.48m/s from a previous maximum of 0.27m/s. Higher walking speed makes the device more useful for locomotion and allows greater independence in society. The Steven Exoskeleton was designed to bridge the gap between seated and standing operation by assisting the user in a new range of postures. This approach expands pilot capabilities while seated and increases overall utility as a tool. This work also discusses a new approach to increase the reliability, and safety of standup and sit-down. Consistent standup and sit-down enables individuals to be self-sufficient with the possibility of full operation without a spotter. The adaptability of this device has enabled testing in laboratory and real world environments with pilots exhibiting a variety of medical conditions. The success of the Steven Exoskeleton and associated control and hardware adaptions moves devices of this nature closer to widespread adoption by paraplegics.

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