On the kinematic design of exoskeletons and their fixations with a human member

A crucial problem in developing robotic exoskeletons lies in the design of physical connexions between the device and the human limb it is connected to. Indeed, because in general the human limb kinematics and the exoskeleton kinematics differ, using an embedment at each connection point leads to hyperstaticity. Therefore, uncontrollable forces can appear at the interaction port. To cope with this problem, literature suggests to add passive mechanisms at the fixation points. However, empirical solutions proposed so far suffer from a lack of proper analysis and generality. In this paper, the general problem of connecting two similar kinematic chains through multiple passive mechanisms is studied. A constructive method that allows to determine all the possible repartitions of freed DoFs across the different fixation mechanisms is derived. It includes formal proofs of global isostaticity. Practical usefulness is illustrated through an example with conclusive experimental results.