Safe teleoperation of a laparoscope holder with dynamic precision but low stiffness.

A laparoscope is a key element in Minimally Invasive Surgery (MIS) as it provides visual feedback to the surgeon. To overcome the drawbacks induced by its manual operation by a human assistant, it can be fixed on the end-effector of a robotic assistant teleoperated by the surgeon: laparoscope displacements are commanded through a master input interface (e.g., joysticks, voice control, etc.) and replicated accordingly at the slave level. In this approach, precision is of high importance to ensure a good operability by the surgeon. This is why the state-of-the-art relies on rigid laparoscope holders with high-gain PID position control, ensuring high static and dynamic precision. However, in the event of undetected obstacles, such stiff systems generate high forces that may cause harm to the patient. Rather, a compliant behaviour is desirable but it leads to a lack of precision when disturbances occur, such as the unknown friction between the trocar and the laparoscope. In this paper we present a “compliant-and-precise” laparo-scope holder with 4 active Degrees of Freedom (DoFs). Its design is based on cable transmission used for haptic interfaces, thus it exhibits very high backdrivability. The paper shows how an intelligent PID position controller can be used to compensate for unknown friction at the trocar while keeping very low PID gains and a satisfactory tracking precision.