Error Evaluation Method of Approximated Inverse Kinematics for Parallel-Wire Driven System – Basic Study for Three-Wire Planar System –

Abstract

[abstFig src='/00280006/04.jpg' width='300' text='Two-degrees-of-freedom planar system using three wires' ] Parallel-wire driven system, a kind of parallel-link mechanism, employs flexible and light wires in place of rigid links. By applying kinematics to parallel-wire driven systems, we seek to obtain the relationship between the end-effector’s position and wire length. Kinematics usually approximates the wire-contacting point of the winding reel (or guiding pulley) in the actuator unit to be a fixed point. Similar kinematic approximations, however, are likely to cause errors in controlling the end-effector position. In this study, therefore, we attempt to evaluate end-effector positioning errors due to inverse kinematic approximations. As the first step, we analyze end-effector positioning errors in two-degrees-of-freedom planar system and propose two methods to evaluate the positioning errors. Then, we conduct two case studies where we compare the errors due to inverse kinematic approximations and effects of wire’s elastic elements in order to confirm effectiveness of the proposed methods for evaluating end-effector positioning errors.