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 upper limb for the shoulder and the elbow was approximated to five degrees of freedom (DOFs) by including the vertical translation of the glenohumeral joint of the shoulder, in addition to the 3 DOFs of the shoulder and 1 DOF of the elbow, which are conventionally used to analyze the motion of the shoulder. The shoulder joint was tilted to avoid singularity problems in the workspace, i.e., 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 of 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 was verified by simulations and experiments.