Abstract: A used deficient-in-rank three-RPS in-parallel actuated manipulator mechanism is studied. Firstly Jacobian matrix is established by using the virtual mechanism method. The principal screws in the third order screw systems are identified by using the conic section degenerating theory. All situations of the pitches of the twist of the end-effector are discussed under two configurations. It is important to know the overall kinematic characteristics of the mechanisms. Therefore, The work presented in this paper is significant for the studies on the robot in trajectory planning and control.

Key words: Kinematic analysis, Parallel robot, Screw theory, Spatial mechanism