Design of an Underactuated Lower Body Exoskeleton Using a Pantograph

This paper presents the design of an underactuated lower body exoskeleton to assist with walking. It reduces the amount of bodyweight going through the user's leg by providing a supporting force to the user that is engaged and disengaged depending on the stage of the gait cycle the user is in. It is engaged when the leg is in stance, effectively pushing between the ball of the foot and the hips, and is disengaged during leg swing. This support force is provided by a linear actuator on each leg that consists of a compression spring, ball screw, and motor. It works by having the motor turn the ball screw, which moves a metal plate to either compress or decompress the spring. The actuator is designed to always be able to extend, to avoid limiting the user's motion. The spring is disengaged while the leg is in swing in order to reduce any impedance to the user's natural stride. The exoskeleton is also designed to minimize any range of motion limitations to reduce its restrictiveness. The exoskeleton was found to be able to provide 19 lbs (85 N) of support to the user per leg.