In context
By mid-2023, single-port surgical robots were gaining traction in minimally invasive procedures, yet transanal endoscopic microsurgery (TEM) remained challenging due to the narrow, rigid instruments that limited dexterity for suturing and knotting. Researchers at Beihang University and Peking University Third Hospital sought to address this with a flexible robotic arm that could navigate the confined workspace of a TEM rectoscope.
What was reported
The team designed a flexible robot based on universal joints and series rods, with a 10 mm diameter arm to fit within the 15 mm operating port of a TEM rectoscope. The arm comprises four universal joints, each with two orthogonal rotational axes, enabling a bending angle of up to 60° at the tip. Four open-loop wires drive the arm's pitch and yaw motions, while a closed-loop tendon system controls the end-effector's gripper and wrist twist.
Kinematic modeling leveraged a constant-curvature assumption for flexible bodies, adapted to the universal joints by treating each joint as a quasi-flexible segment. The authors derived forward kinematics and proposed an optimization method to compensate for cumulative orientation errors (γ) that arise because universal joints lack axial rotation. This correction adjusts the bending direction angle of subsequent joints, improving end-effector positioning accuracy.
Experiments using an optical tracking system showed the robot's absolute positioning error was less than 6.00 mm, with repeated positioning error under 3.00 mm. The master-slave control method was implemented and validated, and the robot demonstrated sufficient load capacity for surgical tasks.
Why it mattered
This work offers a practical solution for enhancing dexterity in single-port TEM surgery, potentially reducing operative difficulty and improving precision. The kinematic optimization method could be applied to other continuum robots with discrete joints, advancing the design of flexible surgical instruments for confined spaces.
"The absolute positioning error of the flexible robot's end is less than 6.00 mm, and the repeated positioning error is less than 3.00 mm."
Source: 《机器人》期刊 (robot.sia.cn) · Published 2023-07-08 · “面向TEM手术的柔性机器人设计与控制”