Kinematic analysis of a 5 DOF upper-limb exoskeleton with a tilted and vertically translating shoulder joint

In this paper, an upper-limb exoskeleton with a tilted and vertically movable shoulder joint is proposed. By analyzing the biomechanics of the shoulder, the motion of the upper limb is approximated by including one degree of freedom (DOF), namely vertical translation of the glenohumeral joint, in addition to the three DOFs that are conventionally employed to analyze the motion of the shoulder. Also, the shoulder joint is tilted to avoid singularity problems in the workspace; by tilting the shoulder joint, the singularity position was placed outside of the normal range of motion. This configuration was analyzed using forward and inverse kinematics methods. Because the shoulder elevation affects all the joint angles, the angles were calculated by applying an inverse kinematics method in an iterative manner. The performance of the proposed upper-limb exoskeleton and analysis methods have been verified by simulations.