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

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.