Simple noninterference mechanism between the pitch and yaw axes for a wrist mechanism to be employed in robot-assisted laparoscopic surgery

Laparoscopic surgery, which is also called minimally invasive surgery, is a surgical technique that is associated with accelerated post-operative recovery. However, it can only be performed by surgeons possessing advanced surgical skills. One of the main challenges in laparoscopic surgery is the restriction of the free motion of forceps because of the limited degrees of freedom imposed by the trocar. Recently, to overcome this problem, many master–slave manipulators with articulated forceps have been used in laparoscopic surgery. The wrist mechanism of the articulated forceps affects the controllability and range of motion of the slave manipulator in the abdominal cavity of a patient. Therefore, improvement of the wrist mechanism of the articulated forceps is important for robot-assisted laparoscopic surgery. This study proposes a new wrist mechanism for using articulated forceps in laparoscopic surgery. The degrees of freedom of the proposed design are provided by motor-driven or manually driven axes employing various wires and pulleys (pitch, yaw, and gripper axes). The kinematic model of this mechanism is decoupled between the pitch axis and yaw axis by a very simple mechanism using arc-shaped guides and wire guide holes. The arc-shaped guides minimize the wire path length error of the yaw and gripper axis wire resulting from the motion of the pitch axis. The optimized position of the arc-shaped guides is decided by the minimal root-mean-square value of the wire path length error. The proposed wrist mechanism has only half the number of parts as compared to the previously developed robotic forceps for clinical use. Furthermore, the effectiveness of the proposed mechanism was demonstrated on a prototype model with a maximum outer diameter of 7.5 mm. Conversely, the disadvantages of the proposed mechanism lie in the transmission mechanism efficiency and no-load input torque.