A Rolling Contact Joint Lower Extremity Exoskeleton Knee

Jonas Beil, Tamim Asfour

Abstract: This paper presents the design, kinematics modeling and experimental evaluation of a rolling contact joint for usage as a knee joint in lower limb exoskeletons. The goal of the design is to increase wearability comfort by exploiting the migrating instantaneous joint center of rotation which is characteristic for rolling contact joints. Two 3D-printed parts with convex surfaces form the mechanism, which is coupled by two steel cables and driven by a linear actuator. This coupling allows rotations around all axis as well as predefined translations. We conducted a kinematic simulation to optimize the shape of the convex joint surfaces and to estimate the expected misalignment between the subject’s knee and exoskeleton joint. In our experimental evaluation we compared forces measured at the exoskeleton interface between subject and exoskeleton prototype with attached rolling contact or revolute joint. The results indicate a reduction of forces and therefore increased kinematic compatibility of the proposed joint design.