Optimal Design of the Laparoscopic Grasper Mechanism with Low Friction and Backlash

Nowadays, the remote technique of minimally invasive surgery is a popular surgical method due to its established benefits to patients compared with conventional open surgery. However, the surgeon's only contact with the operated tissue or organ is through his instrument, so he feels less. This study focuses on the numerical optimization of the laparoscopic grasper mechanism designed at the TU Delft to achieve its best mechanical properties. The design of the laparoscopic grasper mechanism is based on the rolling kinematic pairs distinguished by minimum friction and backlash compared to the conventional revolute kinematic pairs. Optimization is aimed at the constant force transmission from the handle to the jaw of the laparoscopic grasper mechanism, independent of the position of the grasper jaw. Constraints on potential energy stored in the driving and compensation springs, their location, and axial force in the connecting rod of the laparoscopic grasper mechanism are taken into account. The outputs of the laparoscopic grasper mechanism optimization show that it is possible to achieve the force transmission from the handle to the jaw of the grasper close to 1, satisfying all constraints. The root mean square of the differences between the force acting on the grasper handle and the grasping force acting on the movable jaw in its whole angular position interval is 0.1112 N. The maximum difference between these two forces is less than 0.35 N (3.5 % of the 10 N grasping force) at the beginning and at the end of the jaw angular displacement interval. In 70% of the whole jaw angular displacement interval, except the 15% subintervals, with the lowest and highest angular displacements of the grasper jaw, the force difference is even less than 0.1 N.