External force self-sensing based on cable-tension disturbance observer for surgical robot end-effector

The external force sensing ability of the end-effector plays a significant role in restricting the refine operation of a surgical robot. This paper proposes an external force self-sensing method based on the cable-tension disturbance observer for a four-degree-of-freedom (4-DoF) surgical robot end-effector, which is actuated by three backdrivable cable-driven series elastic actuators (BCDSEAs). First, the design of the surgical robot end-effector is introduced with the experimental prototype of a 1-DoF flexible finger joint. Second, four kinds of dynamic models of the flexible finger joint are established and experimentally identified. A joint angle estimator is proposed based on a simplified dynamic model. Then, a closed-loop motion control method for the flexible finger joint is proposed. Third, a driving cable-tension estimator is constructed as the benchmark for the cable-tension disturbance observer under free motion. Meanwhile, an external force self-sensing estimator is proposed based on the motion control strategy and the cable-tension disturbance observer. Finally, the experimental results of joint tracking control present a good performance. The compensation algorithm for the external force under free motion is studied to reduce the system error. The experimental results of the external force self-sensing show an overall estimation accuracy of 85.97% with a range of 0.10–2.00 N.