Abstract: The nonlinear relationship between the cable end tension on four-cable-driven under-restrained parallel manipulator with 6 DOFs and the work platform displacement is deduced by using catenary equation. Therefore, the incremental expression of the resultant force on the work platform exerted by cables is formulated in terms of the work platform displacement. Based on the characteristic feature of better generalization and learning ability of least square-support vector mechine, small-sample data in the workspace are fitted. Stiffness matrix is reported at a point and the stiffness distribution in three translation directions is depicted in the main working planar surface. After searching for the weakest point, the mechanism is optimized based on the global optimization ability of least square-support vector machine. The results show that the stiffness of the transverse translation direction is weaker, and decreasing the ratio of the length and the width of the mechanism can effectively increase its stiffness.

Key words: Cable-driven under-restrained parallel manipulator, Catenary, Least square-support vector machine, Static stiffness