Towards accurate motion compensation in surgical robotics

This paper proposes a method for accurate robotic motion compensation of a freely moving target object. This approaches a typical problem in medical scenarios, where a robotic system needs to compensate physiological movements of a target region related to the patient. An optical tracking system measures the poses of the robot's end-effector and the moving target. The task is to track the target with the robot in a desired relative pose. Arbitrary motion in 6 DoF is covered. The position controller of the medical light-weight robot MIRO is enhanced by a Cartesian displacement observer. The proposed observer feedback preserves the dynamics of the robot, while achieving high accuracy in task space. The target object is equipped with an inertial measurement unit in addition to tracking markers. Target sensor data is fused by an extended Kalman filter in a tightly coupled approach. The robot control and the target tracking in the task space aim to combine accuracy, dynamic performance and robustness to marker occlusions. The algorithms are verified with the DLR MIRO, an experimental target platform, and a commercial tracking system. The experiments demonstrate rapid convergence to desired Cartesian poses and good dynamic tracking performance even at higher target motion speed.