Further Development of a Backdrivable Linear Axis for Collaborative Laparoscopic Surgery

Kurzfassung

This thesis presents a further development of a mechanical interface for connecting standard laparoscopic instruments to the DLR MIRO that was previously developed at the institute. The system enables a switch between two control modes: a handson robot-guided manipulation of the instrument as well as a full telemanipulation capability with an actuation of the tooltip by removing the instrument handle and connecting an adapter. During hands-on manipulation, the interface is operated in conjunction with the gravity compensated MIRO with a virtual remote center of motion constraint at the fulcrum point. It provides the surgeon an additional linear degree of freedom for inserting the instrument and also retains the rotational degree of freedom by rotating the handle knurl. The linear motion is enabled by a three-stage telescopic mechanism that is driven by a pinion and rack actuation and a servo motor. To make the system backdrivable and transparent, the interaction forces with the surgeon at the instrument handle are measured with an ATI Mini45 force sensor in an effort to control the force component along the instrument shaft axis to zero. Experiments revealed considerable improvements to the minimum breakout force required to overcome initial static friction. The capability to measure grasping forces of up to 10 N during telemanipulation via a Kern CK 10-Y1 load cell was additionally integrated. The grasping force was computed based on a prior characterization of a laparoscopic grasper, where a linear relationship between grasping force, pulling force on the instrument pin and grasper opening angle was found. Experiments revealed that future modifications to the sensing concept are required to improve its accuracy.