Dynamic modeling of coupled tendon-driven system for surgical robot instrument

This paper is the study of a surgical instrument which directly performs MIS(Minimally Invasive surgery) on a patient, instead of a surgeon. The instrument used in robot assisted laparoscopy adopts a tendon driven mechanism so that it generates hand-like surgical motion through aperture of trocar. To create a high DOF of motion in restricted spaces, cable systems for end-effector have been organized by serial kinematic chains which can cause interference among joints sharing same axis. Also, to prevent the elongation of any cable, composited and pre-extended cables, which show nonlinear characteristics, are used in surgical instrument tendon system. As aforementioned difficulty and complexity, there are not many studies about measuring or estimating the operating force of instruments without sensors, which is needed for safety but still impossible in commercial systems. This paper derives governing a dynamic model of a coupled cable pulley structure while considering the material tensile characteristics of the cables. The derived model can estimate the operating force on end-effector as well as states of all inner pulleys without encoders. This paper proves the availability of proposed methodology with comparison of numerical analysis and the experimental test of 2 DOF serial kinematic chained cable pulley link apparatus.