Design and development of a semi-rigid hip exoskeleton

Robotic exoskeletons can reduce metabolic cost of walking in healthy individuals and populations with gait impairments. About 40% of the metabolic cost comes from the hip muscles. Different groups have been developing rigid exoskeletons and soft exosuits that assist the hip. Assisting at the hip has the advantage that the system mass is positioned closed to the center of mass, which minimizes the penalty of carrying mass. Soft exosuits have the advantage that they allow greater freedom of movement. However, soft exosuit often cannot apply the same torque magnitudes as rigid exoskeletons, and they rely on friction with the skin to remain anchored. We developed a semi-rigid hip exoskeleton for an existing actuation unit system. The exoskeleton does not have a rigid joint, so it allows full freedom of movement. The waist-belt and thigh pieces are semi-rigid. As a consequence of this, they do not solely anchor to the wearer via friction and compression, but they also stay locked on the body as a consequence of the moment from the actuation. We developed a temporal controller that allows applying a sinusoidal extension and flexion moment as a function of stride cycle percentage. The actuation unit delivers the extension moment. A set of antagonistic springs delivers the flexion moment. This new design will be tested in experiments aimed at developing faster human-in-the-loop optimization algorithms. We believe the semi-rigid design can have advantages in comfort in patient populations because it requires less friction and compression than soft exosuits