Stiffness analysis and optimization of parallel robots used in secondary mirror mount for telescope

This paper presents the stiffness analysis and design of some 3-DOF parallel robots used in second mirror mount for telescope. First, based on the Screw Theory, we designed dozens of structure types, and in this study we picked 3 types, RCU, PUU, and UCU(UP). Second, their stiffness against gravity was analyzed by finite element analysis (FEA) method. The key issues of how the stiffness varying with height angle were investigated. Finally, the regular pattern of stiffness variation with radius ratio of the moving and the static platforms was examined. Study finds: Under low height angles, the stiffness of 3-DOF parallel manipulators is much worse than 6-DOF parallel manipulators; Adding constraining leg can significantly improve the stiffness of 3-DOF parallel manipulators; The stiffness values of 3-DOF parallel manipulators are highly affected by the radius ratio of the moving and the static platforms, and this will provide guidance for optimal design.