Design and Manufacturing of a Multi-Degree of Freedom Hip Exoskeleton for Balance Assistance

Lower limb exoskeletons are becoming a more common tool for mobility assistance. While many assist in walking by decreasing metabolic cost, few exoskeleton designs focus on assisting with dynamic stability. Reducing metabolic cost is important, but impaired users must maintain balance to utilize exoskeleton assistance. One of the most important strategies in maintaining balance while walking is to control foot placement using multi-degree of freedom rotation of the hip joint. A hip exoskeleton must be actuated in both the sagittal and frontal planes to help in foot placement by providing swing phase torque for hip flexion/extension and abduction/adduction. The few hip exoskeleton designs that focus on user stability by including actuation in both sagittal and frontal planes (2-DOF), made sacrifices in weight and practicality to provide high levels of assistance. This thesis puts forward a novel 2-DOF hip exoskeleton design aimed at a lower level of assistance, appropriate for swing phase only, to reduce the exoskeleton's complexity and weight while maximizing its responsiveness. The actuators powering the assistance are quasi-direct-drive and have a high torque to weight ratio. By being backdriveable, these actuators provide mechanical transparency and ensure responsiveness during use. Beyond actuators, the exoskeleton incorporates strategic mechanical decisions to minimize weight. This thesis explores reinforcing 3D printed parts with carbon fiber tape as a replacement for traditional carbon fiber casts. Material tests on reinforced specimens show that it is a legitimate prototyping alternative to conventional carbon fiber layups. Finally, component geometry is optimized to avoid oversized parts while maintaining safety factors for expected stresses. The resulting design represents a 2-DOF powered hip exoskeleton template for testing control algorithms that affords hip-driven, stability assistance during walking.M.S