Proof of concept for a wrist mechanism for articulated forceps for use in robot-assisted laparoscopic surgery

Abstract

Laparoscopic surgery is a minimally invasive surgery that accelerates postoperative recovery, but it can only be performed by surgeons with advanced surgical skills. One of the main difficulties in laparoscopic surgery is the restriction of free motion of the forceps because of the limited degrees of freedom by the trocar. Recently, many master-slave manipulators with articulated forceps have been used in laparoscopic surgery to solve this problem. The wrist mechanism of an articulated forceps affects the controllability and range of motion of a slave manipulator in a patient's abdominal cavity. Therefore, it is important to improve upon the wrist mechanism of articulated forceps for robot-assisted laparoscopic surgery. This paper aims to propose a new wrist mechanism for articulated forceps to be used in laparoscopic surgery. The degrees of freedom of the proposed design are three motor-driven axes that use wires and pulleys (a pitch axis, yaw axis, and gripper axis) and a roll axis driven by manual rotation of the forceps shaft. In the proposed mechanism, the offset distance between the pitch and yaw axes was reduced. The offset value, i.e., 5.95 mm, is shorter than the maximum outer diameter 7.5 mm of the wrist mechanism. Singularity configurations of the wrist axes are avoided near the standard working posture by configuring the pitch and yaw axis. There are few parts and it is simple as compared to the previously developed clinical use robotic forceps. Furthermore, the effectiveness of the proposed mechanism was verified by tests. The range of pitch motion is ± 90°, yaw motion is ± 85° (or ± 90°), and gripper motion is 60° (or 50°). The transmission efficiencies are from about 55 to 75%. The grasping force and torque are more than 5 N and 70 mNm.

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

“…The optimized position of the arc-shaped guides is decided by the minimal RMS of the wire path length error. The proposed wrist mechanism has only half the number of parts as compared to the previously developed clinical use robotic forceps [5,7]. Furthermore, the effectiveness of the proposed mechanism was demonstrated by using a prototype model with a maximum outer diameter of 7.5 mm.…”

“…The wrist mechanism consists of a supporting part, a pitch part, and a part each for the right finger and left finger for an end effector, supporting shafts, and stainless wires (not shown). The shape of the pitch part is roughly the same as that employed in a previous work [7]. If the wire path that bends at the center of the pitch axis can be constructed, the path length of the 2nd-axis and 3rd-axis wires accompanying the pitch axis motion does not change.…”

“…[mm] [mm] Figure 13 shows the mechanical design of the proposed noninterfering wrist mechanism, and Table 1 lists the specifications. The maximum outer diameter is 7.5 mm, which is equivalent to that of the conventional wrist mechanisms used in articulated forceps for robot-assisted laparoscopic surgery [5,7]. The offset distance between the pitch axis and the yaw axis is 6.95 mm.…”

“…In addition, the rotation radius of the wire tip around the pitch axis is r 2 = 9.45 + 0.45/2 mm . Table 2 presents a comparison of the components with the parts of the conventional wrist mechanism [7]. Figure 14 shows the wire route and coordinate system.…”

“…However, this is an interference mechanism. Furthermore, the wrist mechanisms reported in previous papers [6,7] and a patent [8] proposed by the author are interference mechanisms. In general, articulated forceps that employ a wire-pulley or gear drive mechanisms or both are interference mechanisms.…”