Wearable devices for physical assistance : enhancing capabilities after stroke and in running

Exoskeletal robots can augment human motor abilities in tasks such as walking, lifting heavy objects, and performing therapies after motor impairing illness or injury. Yet, developing exoskeletal robots that can safely interact with human operators is a difficult engineering challenge. As a result, many commercially available exoskeletons are expensive, limiting access to them. Limited access implies limited usefulness, particularly for motor impaired populations that might benefit from increased volumes of robot-aided therapies. Exosuits simplify exoskeletal robot development by foregoing the rigid linkages that normally act as a transmission and apply forces generated by actuators directly to the human body. Removing the rigid linkages removes components and mass from the robot, reducing cost and some safety concerns. Passive exoskeletons and exotendons further reduce components and simplify safety considerations using springs and clutches in lieu of electronically controlled motors and pneumatics. In this thesis, we leverage insights from neuromechanics to design, build, and test simple assistive devices that aid post-stroke upper extremity movements and improve running economy. In the first part of this thesis, we design, build, and test in both unimpaired and stroke impaired populations novel inflatable exosuit actuators to support shoulder abduction which can increase reachable workspace area in the unassisted horizontal plane in stroke survivors. The exosuit actuators, or "exomuscles, " we developed are pneumatically actuated bladders that push the arm away from the torso when inflated to support shoulder abduction. We validate that our exomuscles reduce the activity of shoulder abductor muscles without impeding range of motion in healthy operators and that they increase reachable workspace area in the unassisted horizontal plane in stroke survivors. We provide data demonstrating that some devices might produce the same effect in healthy operators, but show diverging effects in a stroke population -- important cautionary data for investigators that primarily validate designs in healthy operators. We also design, build, and characterize in healthy participants an inexpensive passive wearable exoskeleton for shoulder abduction support that can be used for take-home assistance. In the second part of this thesis, we develop a passive wearable exotendon that improves healthy human running economy. Our exotendon is constructed of a single length of natural latex rubber attached to the shoes, and acts as an energy recycling spring intended to assist the hip muscles in swinging the leg during running. Exotendon use increases the energetically optimal stride frequency of running, allowing runners to select faster stride frequencies that reduce the mechanical effort required to redirect the body's center of mass. This exotendon is a minimally complex, inexpensive device that also sheds light on some of the behavioral adaptations that humans employ to make use of wearable assistive devices. The work presented in this thesis leverages neuromechanical insights to create wearable, inexpensive devices that aid in post-stroke upper extremity movement and in healthy human running. In turn, some of these devices led to new neuromechanical insights. These low-cost, wearable alternatives to existing assistive devices may enable further discoveries about long-term use of assistive devices and the effects of larger doses of assisted therapies

Keywords: Mechanical Engineering.
Advisor: Okamura Allison
Collins Steve (Steven Hartley) 
Hawkes Elliot