The kinematic analysis and stiffness optimization for an 8-DOF cable-driven manipulator

Abstract

This paper proposed an 8-degrees-of-freedom (8-DOF) cable-driven robotic arm (CDRA) composed of four identical 2-DOF cable-driven joints with variable stiffness. The proposed cable-driven joints are equipped with variable stiffness devices to increase the stiffness adjustable range. Therefore, an inverse displacement algorithm is proposed for this redundant robotic arm using the conjugate gradient method. A rotation control function is employed as an objective to minimize due to the character that the cable-driven joints has a larger stiffness range when the joint angle is small. With such algorithm, the joint angles will have a larger stiffness range. Then, the stiffness of the CDRA is analyzed with the body manipulator Jacobian employed. An optimization algorithm using similar conjugate gradient method is proposed to obtain the desired stiffness. Low cable tension level could be obtained with a "tension level index" employed in the optimization. A simulation of the algorithm is conducted and the result shows that such method is effective and computational efficient.