Criteria for the design of manipulator arms for a high stiffness-to-weight ratio

Abstract

Design aspects of a six degree-of-freedom high-accuracy manipulator are presented. The manipulator arm (called the UTI-arm) comprises four revolute and two prismatic joints. The mechanical design of the manipulator is aimed at obtaining high accuracy and a high stiffness-to-weight ratio of the links. Prestressing of mechanical elements is performed to transform strength to stiffness. Design of links under tension load is carried out to enhance bending stiffness. In the past, researchers have reported inefficiency of prismatic joints due to their high compliance. Compared to a uniform thin-walled tube, prismatic joints used in this design provide an isotropic, higher bending stiffness with a relatively low loss in torsional stiffness. Experiments were conducted to verify the theory presented for calculating torsional stiffness of such joints. A finite element model was also used to validate the model. The mechanical design of the arm is presented in detail in view of the proposed prismatic joint cross section and the prestressing effects.