Design and analysis of a spherical humanoid neck using screw theory

This paper presents a simple methodology for the quantitative and qualitative analysis of the performance of spherical parallel platforms. The presented method is oriented to get a mimetic relation between the human motions and the spherical mechanism motion. The quaternion formulation is used to represent the possible rotations, showing the workspace as a tridimensional solid object. The graphical intersection of the singularities of the platform with its workspace allow an study of the mechanism kinematics. To explain this method, the kinematics of the human neck is plotted, and the analysis of a suggested 2UPS-1RU (with two legs with Universal, Prismatic, Spherical kinematic chain and one leg with a Rotational-Universal kinematic chain) parallel platform is presented. Finally, some results about the forces on actuators for the resulting design of the spherical platform are shown