Endoscopic 3DoF-Instrument with 7 DoF Force/Torque Feedback

Minimally invasive surgery (as previously discussed) is an operation technique advantageous for patients. However, surgeons have to contend with a number of disadvantages. With the development and commissioning of a robot supported, prototypic minimally invasive robotic surgery (MIRS) instrument the intracorporal manipulability as well as surgeon’s immersion will be enhanced. This paper will give an outline of the endoscopic instrument consisting of 3 DoF actuation unit, 2 DoF joint, 7 DoF Force/Torque sensor, and functional end. The distal end of the instrument (cf. Fig. 1) consists of a cable driven 2 DoF universal joint, a 6 DoF force/torque sensor for measuring instrument interaction forces/torques, and a gripping DoF with integrated, distal gripping force sensor (1 DoF). The cable driven universal joint allows a ±40◦ motion in two orthogonal planes. Together with the wrist rotational DoF of the supporting robot (MIRO see Fig. 2 [1]) the universal joint forms a spherical wrist with intersecting axes. Restoring two DoF articulation inside the patient eliminates movement restrictions in the workspace and therefore reestablishes full dexterity and increases manipulability. The drive cables form two closed loops which allow for coupled linear motion of the universal joint. Minimally invasive suturing (intracorporal viscerosynthesis) is one of the most difficult and time consuming tasks in conventional MIS. To limit the number of instrument changes, MIRS instruments should have the ability to not only delicately grasp tissue, but also to strongly and securely hold needles. Kitagawa et.al. reported ideal knot tying forces between 1 N and 4 N for commonly used suture material [2]. Assuming a worst case friction coefficient of μ0 = 0, 1 between needle and holder, a grasping force of up to 40 N is required. Currently, only a generic gripper shape exists. However more specialized geometries are being developed in cooperation with industrial partners. The spatially separated arrangement of user input station and robotic manipulator prevents any direct haptic feedback from the operation site. In order to provide direct feedback of tissue manipulation forces to the surgeon, these have to be measured at the operation site. The measurement range should be larger than the knot tying force described above. However, physical constrains, particularly electrical noise, necessitates a tradeoff between resolution and measurement range. Tissue penetration forces of commonly used suture needles were studied in depth by numerous research groups (e.g. [3, 4]) to establish minimally required resolution of the manipulation force