Collaborative framework for robot-assisted minimally invasive surgery using a 7-DoF anthropomorphic robot

In this paper, we propose a control framework for robot-assisted minimally invasive general surgery (RA MIS) for physical human-robot collaboration using a redundant 7-DoF serial robot. When a redundant manipulator is used in RA-MIS, the control system implemented must guarantee that the surgical tool always goes through the trocar, i.e. the medical instrument placed at the incision point on the patient's body. In addition, the redundancy of the robot can be exploited to implement a physical human-robot collaborative strategy, allowing the medical staff and robot to work in a shared common workspace without affecting the performances of the surgical task, through a null-space compliance control strategy. However, classical null-space compliance laws are defined in joint coordinates, which have some limitations. First, an arbitrary desired joint configuration is rarely contained in the robot's null-space, making the desired configuration unattainable. Moreover, the joint coordinates are not a direct representation of the robot's null-space, which limits its exploitation. The control framework proposed in this paper is performed at the torque level. A manual motion mode is used to calibrate the trocar position before executing the task. Then, a cartesian compliance control strategy is activated during execution of the surgical task, enabling the robot to autonomously execute the surgical task while the tool orientation is calculated with respect to the trocar position. Furthermore, in order to preserve the surgical task when desired or undesired contacts occur, the null-space of the main task, i.e. surgical task, is used to implement a compliant motion in the robot's body. The compliance control approach is defined in the swivel coordinates, which effectively represent the null-space of the robot, in order to easily restrict the swivel angle motion based on joint limitations or on any other physical constraint existing in the operating room. Finally, we evaluate our control framework using a robotic system including the KUKA LWR 4+ robot, demonstrating the feasibility of the null-space compliance control approach while preserving the accuracy of the surgical task. (C) 2018 Elsevier B.V. All rights reserved.