Accurate Pose Estimation for Comanipulation Robotic Surgery

Robotic comanipulation provides a cost-effective solution to telesurgery when remote operation is not strictly necessary. Within the field of laparoscopic surgery, the comanip-ulation scenario is only recently being exploited commercially in the form of lightweight backdrivable systems. A passive wrist backdrivable robot does not require preoperative alignment with the incision that acts as a fulcrum around which the laparoscopic instrument pivots. Moreover, backdrivable systems can be comanipulated by the user without the need for expensive force sensors. Unfortunately, most backdrivable systems only provide limited accuracy when measuring the end effector pose from their joint encoders. Accurate knowledge of the end effector pose is required to estimate the the instrument tip and fulcrum position. This work presents a robust method to improve localisation of the pose of the end effector of a backdrivable robot. The method fuses optical tracking with robot proprioception by means of an unscented Kalman filter and is robust against intermittent occlusions of the line of sight. The algorithm is experimentally validated by analyzing its initialization behavior and accuracy when estimating the instrument tip and fulcrum position. An accuracy of
$1.58\pm 0.157$
mm and
$0.699\pm 0.389$
mm is achieved when estimating the instrument tip and fulcrum position respectively, which makes the algorithm suitable for advanced guidance schemes in comanipulation robotic surgery.