The ability to walk is perhaps the most common indicator of mobility and independence. Regrettably, a large portion of the population is experiencing a loss in mobility due to aging and/or chronic health conditions. There is thus an urgent need to develop systems that would help preserve mobility for individuals in need. One promising solution to this growing problem is Walking Assist Exoskeletons. Current devices mostly rely on powered systems to provide walk assist by applying complementary torques about lower limb joints. Whereas these exoskeletons have achieved technological breakthroughs, they are not without limitations. In response, developments of passive alternatives are now emerging and have demonstrated the potential for simple, cost-effective devices. Aligned with this progress, the following study proposes the development of a passive exoskeleton that enhances mobility during stance and walking. This is achieved through an unpowered seat mechanism that produces an upward force on the pelvis of the user. Two analytical models are developed to predict its behavior, by evaluating the effect of increasing the stiffness of the mechanism, as well as predicting device kinematics and its resulting assistance throughout a gait cycle. A human-scale proof of concept prototype was fabricated and tested using motion capture equipment and load cells. The results validated the proposed design, which provided an upward stance force between 9.41% and 26.18% of body weight for six levels of spring stiffness. The exoskeleton also provided an upward peak walking force between 14.02% and 27.52% of body weight for five levels of spring stiffness.
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Walking Assist Exoskeletons are a class of assistive devices intended to restore a person's independence. Current powered Exoskeletons suffer from limited usability due to power demands. Furthermore, motors and battery packs are often cumbersome and heavy. A passive walking assist device is one that does not rely on an external power source, instead drawing energy out of the gait cycle itself. This study proposes the development and initial testing of a passive ankle exoskeleton intended to provide a plantarflexion torque assist during the push off phase of gait. The design incorporates a Pneumatic Artificial Muscle as a non-linear elastic element to store and release energy during walking. The device also integrates a novel clutch mechanism design to engage and disengage the spring element about the ankle joint during walking such that it does not impede the ankle motion during swing phase. Mechanical testing demonstrated the prototypes ability to function adequately over the natural range of an ankle joint and generate an ankle torque equal to at least 25% of natural ankle torque during normal walking. Using motion capture and electromyography systems, human testing was performed to examine the gait kinematic and muscle activation when the device is worn, unilaterally. The preliminary results show that the exoskeleton is able to reduce the activation of the calf muscles on the limb wearing the device. However, a decrease in ankle joint range of motion is noted in the limb with the device, and, to a much lesser extent the leg without the exoskeleton.
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