Kinematic Characteristics of 3-UPU Parallel Manipulator in Singularity and Its Application

This paper focuses on the kinematic characteristics of the 3‐UPU (universal‐prismatic‐ universal) parallel manipulator in one of singular configurations. The motion of the moving platform is analyzed by changing the layout of the universal joints. A layout of universal joints in the singular configuration is discussed in detail by deriving the kinematic and constraint equations. Solving the equations, the kinematic characteristics in such case is obtained. At the same time the kinematic characteristics is simulated by the commercial software and the results of the simulation verify it. Based on the kinematics characteristics of it, the application of the singular configuration is presented. And a compound limb which can translate freely along a circular path is presented. Finally, the some new 2‐DOF (degree of freedom) planar parallel translating manipulators whose orientation can remain constant are put forward by the compound limb. The passive joints of the new 2‐DOF planar parallel translating manipulators are universal joint and the struts of it do not bear the bending moment. It gives the planar parallel manipulator a good architecture to resist the force which is perpendicular to the kinematics plane.