Utilizing Elasticity of Cable-Driven Surgical Robot to Estimate Cable Tension and External Force

Cable-driven robots enable compact design by allowing actuators to be mounted away from joints. This kind of actuation is desired in surgical robots. The cables in these robots must remain under tension at all times in order to have optimum performance. Thus, the knowledge of initial value of cable tension is significant. Moreover, in surgery, haptic feedback is vital for diagnosis of healthy tissue and to prevent damaging tissue with excessive force. In this paper, cable pretension was estimated indirectly by estimating stiffness parameter of cables. Then, external forces acting on the robot were estimated in all four quadrants by using cable stretch and dynamic-based methods utilizing system dynamics and unscented Kalman filter (UKF). We assessed the effectiveness of these methods on the third link of Raven-II surgical robot platform. From experiments with the tension estimation technique, it can be determined if the cable pretension is in the safe range. Also, both the cable stretch and UKF-based methods can be used to estimate external forces on all quadrants.