Stiffness Analysis of Parallel Manipulators with Preloaded Passive Joints

Abstract. The paper presents a methodology for the enhanced stiffness analysis of parallel manip-ulators with internal preloading in passive joints. It also takes into account influence of the external loading and allows computing both the non-linear “load-deflection ” relation and the stiffness ma-trices for any given location of the end-platform or actuating drives. Using this methodology, it is proposed the kinetostatic control algorithm that allows to improve accuracy of the classical kine-matic control and to compensate position errors caused by elastic deformations in links/joints due to the external/internal loading. The results are illustrated by an example that deals with a par-allel manipulator of the Orthoglide family where the internal preloading allows to eliminate the undesired buckling phenomena and to improve the stiffness in the neighborhood of its kinematic singularities. Key words: modeling, parallel manipulators, external loading, internal preloading, passive joints.