Feasible instantaneous motions and kinematic characteristics of a special 3-DOF 3-UPU parallel manipulator

This paper studies all the feasible instantaneous motions and kinematic characteristics of a special 3-DOF 3-UPU parallel manipulator. In every UPU branch two middle revolute pairs are perpendicular to each other. This mechanism has three instantaneous translational degrees of freedom, but it is not a normal 3D translational mechanism. This paper analyzes all feasible instantaneous motions of this special mechanism in depth by using the reciprocal screw and principal screw, and obtains the plane representation of the finite-and-infinite pitches of the third special-three-system screw. The analysis discovers some interesting and special characteristics of this mechanism. All of the results are significant for enriching the mechanism theory and useful for mechanism design.