Robotic Knot Tying for Minimally Invasive Surgeries

There have been many innovations introduced in securing tissues, but suturing with secure knots remains the most popular and cost effective method. However, knot tying demands higher level of skill on the surgeon, especially in the minimally invasive context. This paper presents the analytical and experimental results of automatic knot tying using an inhouse surgical robot with emphasis on the placement of the knot and tension regulation. The problem is decomposed to two parts: knot placement and knot tension control. The knot sliding condition is first obtained based on a simplified model of half knotted suture, and motion trajectories for the robots are proposed to minimize tearing trauma of the tissue while properly place the knot. The second half the paper considers the automatic tension regulation in the knot, which is usually difficult for the surgeon to achieve accurately. By using a cost effective means for tension measurement and applying the explicit force control algorithm with active damping, we are able to achieve stable and robust tension regulation. Experimental results are presented to demonstrate efficacy of the proposed algorithm.