Deformation analysis of belt-formed pulley to adjust joint stiffness of tendon robot

A belt-formed pulley is a nonlinear spring device. Inserting the belt-formed pulleys into routes of wires, joint stiffness of a tendon-driven robot can be varied depending on internal force among wires. The system using belt-formed pulleys has many advantages such as low cost, low friction, light and so on, compared with other devices to vary joint stiffness. However, little is known about joint-stiffness property of the system using belt-formed pulleys. In this paper, we analyze deformation of belt-formed pulley by using three approximate models. Based on comparison between results of simulations and experiments, we present the usefulness of the proposed models. Finally, the forward kinematics to obtain a joint angel from wire length is discussed for a one-link manipulator system.