Kinematic Analysis and Design of a Novel Shoulder Exoskeleton Using a Double Parallelogram Linkage

Abstract

The design of an innovative spherical mechanism with three degrees-of-freedom (DOFs) for a shoulder joint exoskeleton is presented in this paper. The spherical mechanism is designed with a double parallelogram linkage (DPL), which connects two revolute joints to implement the motion as a spherical joint, while maintaining the remote center (RC) of rotation. The design has several new features compared to the current state-of-the-art: (1) a relative large range of motion (RoM) free of singularity, (2) high overall stiffness, (3) lightweight, and (4) compact, which make it suitable for assistive exoskeletons. In this paper, the kinematics and singularities are analyzed for the spherical mechanism and DPL. Dimensional analysis is carried out to find the design with maximum RoM. The new shoulder joint is finally designed, constructed, and integrated in a four degree-of-freedom wearable upper-body exoskeleton. A finite element analysis (FEA) study is used to assess the structural stiffness of the proposed design in comparison to the conventional 3R mechanism.