The new methodology denes the task of the linkage in terms of the movement of a spatial
three-link serial chain, which is then constrained to dene the six-bar linkage. The focus is
on three spatial chains constructed from revolute, or hinged joints, and prismatic, or sliding,
joints. These chains are denoted as the RRR, the RPR, and the PRP spatial serial chains.
The spatial six-bar linkage is obtained by nding points in the moving links that lie on a
sphere, which means that they can be constrained by a link connecting two spherical, or ball
joints, known as an SS dyad.