Mobility Analysis of Coupled System of Upper Limb Exoskeleton and Human Arm

Misalignment between human and exoskeleton joints is an inevitable challenge that hinders user’s safety, comfort, and assistance efficiency. It also results in undesired interaction forces that are applied to the human body limbs, further affecting the safety of the user. In this context of the design of exoskeletons and the study of misalignment effects—through mobility analysis, the overall motion of the coupled model of the exoskeleton and the human limb is proposed to be studied. This paper focuses on the mobility analysis of a coupled system of a 2-DOF (degrees-of-freedom) upper-limb exoskeleton for rehabilitation purposes of the human arm. In this work, planar rehabilitation exercises are used as tasks to be followed by the exoskeleton. These possess only planar motion, (i.e., parallel to sagittal plane) consisting of 2-DOF, i.e., flexion–extension movement of both shoulder and elbow joint. Two different configurations (type I and type II) of the upper limb exoskeleton are used to demonstrate the proposed methodology. The type II mechanism consists of redundant DOF that are used to address the problem of misalignment associated with the shoulder joint. The coupled systems of both types are further analyzed and compared in terms of their performance through screw algebra.