Design of a Large Workspace Passive Spherical Joint via Contact Edge Design

This paper presents the design of a compact ball and socket type spherical joint that makes use of passive elements to increase the range of motion to greater than a hemisphere with infinite roll capacity. We discuss the limitations of typical spherical joints due to simple geometric considerations, and how the addition of redundancy, passive elements, and multiple contacting surfaces of differing geometry can increase the workspace of these joints. We discuss the relationship between kinematics, mechanical conditions (e.g. friction and contact forces) under quasistatic motion, and geometry required to achieve the increased range of motion. Furthermore, we provide a metric for assessing the viability or benefit of a potential design. Finally, we validate one of our designs with a physical prototype and demonstrate its achievable range of motion.