One of the major functions brought by robots in Minimally Invasive Surgery is endoscope holding. This consists, for the user, in placing the camera at a desired location which the robot will maintain still once he/she releases it. This behavior is usually achieved with rigid position servoing, leading to possibly high forces generated and safety issues. Model-based weight compensation is an alternative solution. However, endoscopic cameras' weight is difficult to model as their gravity parameters can change during the same surgery. In this paper, an algorithm is presented as an option to cope with this variability in the gravity model without using rigid position servoing. The surgeon first positions the camera in a comanipulation mode (gravity compensation). When he/she releases the camera, if the gravity model is not accurate, the endoscope presents a drift. In this case, a controller brings the endoscope back to its release position by combining low gain position control and model adaptation. Once stabilized, the system is switched back to a zero-stiffness mode. Two in-vitro experiments were performed in which a user manipulates an endoscope whose configuration of mass is changed. In one case, the mass in the gravity model was set to half of the actual one. In the second case, a variable weight was attached to the endoscope. The algorithm successfully updated the model for each experiment reducing position errors by 95% and 57%, respectively.

Classic Minimally Invasive Surgery (MIS) is an ergonomic burden for assistants and surgeons. The former need to adopt uncomfortable positions for hours while holding a camera to track the latter’s gestures inside the patient. This incurs assistant’s muscle fatigue which can lead to tremor or drift of the video feedback. A backdrivable robotic holder can be attached to this device in order to compensate its weight. This allows the user to place the camera at a desired position which the robot will steadily keep once he/she releases it. However, endoscopic cameras present difficult-to-model accessories whose gravity parameters can change during the same surgery. If these changes are not foreseen by the gravity model of the robot this results in a fall of the endoscope each time it is released. Therefore, it is desired to firstly detect if there is a fall in order to be able to correct it. In this article a fall detection method for a comanipulated robotic endoscope holder is proposed. It evaluates smoothness of the robot end effector trajectory to identify whether the user manipulates the instrument or it has been released and poorly compensated. An experiment was carried out with 10 subjects where 240 releases of the endoscope were performed while it was poorly compensated. The algorithm succeeded to detect the falls with sensitivity up to 99.17%.

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.