Assistance to laparoscopic surgery through comanipulation

Abstract

Traditional laparoscopic surgery brings advantages to patients but poses challenges to surgeons. The introduction of robots into surgical procedures overcomes some of the difficulties. In this work, we use the concept of comanipulation, where a 7-joint serial robotic arm serves as a comanipulator and generates force fields to assist surgeons.In order to implement functions like instrument gravity compensation, identifying real-time trocar position with respect to robot base is a prerequisite. Instead of obtaining trocar information from the registration step, we propose a robust trocar detection and localization algorithm based on least square method. Both in-vitro and in-vivo experiments validate its efficiency.Considering the characteristics of laparoscopic surgery, i.e., relatively large workspace and flexible operating objects, viscous fields are employed. To better adapt to different motion, we use a variable viscosity controller. However, this controller encounters an instability problem, which is analyzed both theoretically and experimentally. A solution of adding a first order low pass filter is proposed to slow down the variation of the viscosity coefficient, whose efficiency is evidenced by a point-to-point targeting experiment.With real-time trocar position known, the “lever model”, a formula describing therelationship of the velocities and forces of different instrument points, can be established. This allows implementing viscosity controller without using noisy signals at the center points of instrument handle and tip. Another point-to-point movement experiment is conducted to compare the features of the controller influence on human motion behaviors.