Toward force detection of a cable-driven micromanipulator for a surgical robot based on disturbance observer

Abstract. Force sensing plays an important role in minimally invasive surgery (MIS). Force sensing makes it possible for the surgeon to feel the tissue properties and apply an appropriate level force and avoid tissue damage. The micromanipulators are compact and to allow appropriate disinfection, it is inappropriate to integrate sensors at the end of the micromanipulator. In this study, a new asymmetric cable-driven type of micromanipulator for a surgical robot was designed, and a joint angle estimator (JAE) was designed based on the dynamical model of the single cable-driven joint. Closed-loop control of the joint angle was carried out by regarding the JAE output as the feedback signal. On this basis, an external force estimator was designed using a disturbance observer (DOB). The experimental results show an average accuracy of the joint angle estimator of about −0.150°, with excellent control precision, the largest absolute error of about 0.95°, and an average error of 0.175°. The accuracy of the force estimator was at a high level during static loading. The estimated accuracy was 94 % at external force is greater than 1 N, and the estimated accuracy was 82 % for an external force of 0.3 N. These results predict that force sensing of a cable-driven micromanipulator in this paper can used to realize the micromanipulator's force feedback of a minimally invasive surgical robot.