Application of Cylindrical Elastic Elements for Stiffness Control of Tendon-Driven Manipulator and Inverse Kinematics Evaluation

A cylindrical elastic elements (CEE) is proposed to vary joint stiffness of a tendon-driven manipulator. The CEE is made of a cylindrical flexible object or rolling of a blade spring. By inserting the CEEs into routes of wires, the joint stiffness can be changed depending on a set of internal forces. However, it is difficult to obtain the solution of the inverse-kinematics for the manipulators with CEEs because of the complexity of CEE´s deformation. This paper presents a numerical solving method for the inverse-kinematics of the one-link manipulator equipped with two CEEs. Using an approximate model of a CEE, we demonstrate the numerical solving method to obtain the wire length from the joint angle and stiffness. The precision of the proposed methods is evaluated by comparison between experimental results and numerical results.