Abstract: The family of [PP]S parallel mechanism can undergo one translational degree of freedom (DOF) and two rotational DOFs, thus having great potential in practical application. The 2-PRS-PRRU parallel mechanism belongs to the family of [PP]S parallel mechanism. Mobility property of the 2-PRS-PRRU parallel mechanism is analyzed by using screw theory and the two finite rotational axes are identified. Parasitic motion of the 2-PRS-PRRU parallel mechanism is studied. It is proved that this parallel mechanism has no parasitic motion. The forward and inverse position kinematics models are established and the analytical solution is obtained. Jacobian matrix of the 2-PRS-PRRU parallel mechanism is obtained. Inverse, forward and combined singularities are identified based on the analysis of the Jacobian matrix. The 2-PRS-PRRU parallel mechanism has great potentials in practical application because of its identified finite rotational axes and zero parasitic motion.

Key words: Kinematics, Parallel mechanism, Parasitic motion, Singularity