Kinematic analysis of Hobermanʹs Linkages with the screw theory

This paper studies the Hobermanʹs linkage consisting of a series of scissor like elements connected by revolute joints. Because every Hobermanʹs angulated element subtends a constant angle during the motion, every angulated link was assumed as a PRRP linkage which has two prismatic joints and two revolute joints. Therefore, the two PRRP linkages of the Hobermanʹs angulated element are individually movable with a single degree of freedom. The mobility was investigated with the method based on the screw theory. It has been proved that the Hobermanʹs angulated element is movable because the terminal constraints exerted to the common joint by the two linkages are equal.