Infinite rotational motion generation and analysis of a spherical parallel manipulator with coaxial input axes

This paper presents a novel framework for the analysis of a 3-RRR spherical parallel manipulator with coaxial input axes (coaxial SPM) with the focus on its infinite rotational motion capabilities and its effects on the manipulator's characteristics. The framework consists of three phases. At first, an approach for obtaining unique solutions of forward and inverse kinematics problems is introduced for setting up univocal relation between coaxial SPM's input joint positions and orientation of its end-effector. At the second phase, a method for generating infinite rotational motions of an end-effector is formulated. The third phase outlines numerical computation procedures of the coaxial SPM's workspaces in the joint and Cartesian spaces, excluding singularity configurations and mechanical collisions of SPM's links during infinite rotational motion. A 3D design model and an experimental prototype of the coaxial SPM is presented and utilized for numerical analysis and experimental verification of the presented framework supplemented by an accompanying video demonstration.