Kinematics and workspace analysis of a 3-CR(Pa)(Pa)R parallel mechanism with an orthogonal layout

The authors report on the kinematics and workspace analysis of a six-dof 3-CR(Pa)(Pa)R parallel mechanism (PM) with an orthogonal layout, which is found to bear various advantageous features. A compact forward-kinematics model is established, leading to a linear univariate characteristic polynomial, significantly reducing the computational cost. Moreover, the velocitylevel kinematics indicates that the rotation and translation of the moving platform (MP) are decoupled, and the mechanism under study can achieve isotropy upon proper dimensioning; furthermore, the forward and inverse singularities are found to be solely dependent on the MP orientation, which can be characterized by six elliptical arcs in the orientation workspace; the study also reveals that the MP can theoretically rotate about any axis for at least +/- 90 degrees before encountering these singularities. Finally, its interference-free workspace is evaluated, indicating that the mechanism under study can offer a relatively large orientation workspace. The foregoing features make the proposed PM potentially attractive in a wide range of applications.