A Needlescopic Wrist Mechanism With Articulated Motion and Kinematic Tractability for Micro Laparoscopic Surgery

Invasiveness of laparoscopic surgery can be further reduced by using needlescopic instruments which diameter approaches that of a hypodermic needle. However, such needlescopic instruments are limited by the lack of wrist mechanisms with precise and sharp articulating motion. In this article, we present a two-degree-of-freedom wrist mechanism with articulating motion and enhanced kinematic tractability for micro laparoscopic surgery. The mechanism consists of two highly curved nitinol tubes serially connected by rotary joints whose axes intersect at a remote center of motion (RCM). Its elasticity is only utilized for introducing through a trocar. Once introduced, the rigid body motions of each tube by the rotary joints generate pivoting motion of the attached end-effector about the RCM point. This allows large reorientation of the end-effector's direction with minimal displacement. The serial link structure of the mechanism leads to analytic solutions for tractable kinematics. The design, manufacturing, and the validation of the kinematics of the mechanism are presented, and the feasibility of the mechanism is demonstrated through the peg transfer test using a teleoperated robot system.