Mobility and kinematic analysis of a special class of 3T1R parallel manipulator

This paper proposes the mobility and kinematic analysis of a parallel manipulator (PM) able to generate a Schönflies motion of its moving platform. This motion consists of a spatial translation (3T) with a rotation about a fixed axis (1R). The manipulator has a fixed base and a moving platform connected by 4 legs. Each leg is a serial kinematic chain with an actuated prismatic joint (P), and two couples of revolute joints (R) with their axes being perpendicular and coplanar (such a couple of R joints forms a U joint). The mobility of the moving platform is analyzed by a procedure based on the screw theory while the forward and inverse position analyses are then dealt with by a vector approach. Finally, the singularities of the motion are inspected.