Numerical Solution Framework of Kinematics for a Tendon-Driven Manipulator Equipped with Cylindrical Elastic Elements

Abstract

To date, many hardware devices to control joint stiffness have been proposed for tendon-driven manipulators. However, the earlier devices presented some problems such as complex structures, increase of friction, increase of inertia, etc. To overcome these problems, we propose the cylindrical elastic element (CEE) to vary the joint stiffness by changing the internal force among wires. By inserting the CEEs into routes of wires, the joint stiffness of a tendon-driven manipulator can be changed depending on the internal force. However, it is difficult to obtain the kinematics because of the complexity of a CEE's deformation. Since a finite element method usually requires much time to calculate, the establishment of a simple CEE model is very important to solve the kinematics. This paper presents a numerical framework to approximately solve the kinematics of a one-link manipulator equipped with two CEEs. First, we propose some approximate models of a CEE and evaluate them. Using the most useful model, we then demonstrate a numerical solving method of the forward kinematics. Next, expanding this solving method, we also provide the inverse kinematics. The precision of the proposed methods is discussed through comparison of experimental results with numerical results.