Kinematic/dynamic analysis and optimization of a 2-URR-RRU parallel manipulator

A 2-URR-RRU parallel manipulator has two rotational degrees of freedom (DOF) and one translational DOF, where U denotes a universal joint and R a revolute joint. The 2-URR-RRU parallel manipulator has promising engineering potentials. However, investigations on its kinematics, dynamics and optimal design are deficient, which tremendously hinders its application. This paper presents the kinematic/dynamic modeling and motion/force performance-based optimization of the 2-URR-RRU parallel manipulator. Firstly two rotation axes and one translation direction are found by mobility analysis based on screw theory. Then forward/inverse kinematic models are constructed for position analysis. Based on the kinematics, dynamics modeling is established through the Newton-Euler method. The Jacobian matrix, which relates the velocity of actuators and that of the end-effector, is deduced to investigate the singularity of the parallel manipulator. Analysis reveals that this manipulator only has inverse singularities, with no forward or combined singularities. In addition, its workspace is obtained with a compromise of main practical limitations. Furthermore, force/motion performance indices are employed for optimization of geometrical parameters. This study brings valuable kinematic/dynamic insights of the 2-URR-RRU parallel manipulator and is fundamental to further research in stiffness analysis and control system design.