Ultra-slender Coaxial Antagonistic Tubular Robot for Ambidextrous Manipulation

TL;DR

This work addresses the need for ultra-slender robotic arms that combine high stiffness with dexterous manipulation in narrow spaces, such as minimally invasive surgery. It introduces a coaxial antagonistic tubular robot (CATR) with asymmetric patterned tubes fixed at the tip, actuated axially to achieve bidirectional bending, and outfitted with tenon-mortise slits to boost stiffness without sacrificing dexterity. The authors develop a kinetostatic framework for a single segment, extend to a dual-segment configuration with 6-DOF reach, and apply Pareto-front optimization to jointly maximize bending curvature $\kappa_M$ and stiffness $EI$, followed by GA-based inverse kinematics for hyper-redundant control. Experimental validation demonstrates accurate push/pull to bending mapping, feasible load handling, rapid IK computation, and MIS-relevant demonstrations, indicating strong potential for ultra-slender surgical tools with enhanced maneuverability and force transmission.

Abstract

As soft continuum manipulators characterize terrific compliance and maneuverability in narrow unstructured space, low stiffness and limited dexterity are two obvious shortcomings in practical applications. To address the issues, a novel asymmetric coaxial antagonistic tubular robot (CATR) arm with high stiffness has been proposed, where two asymmetrically patterned metal tubes were fixed at the tip end with a shift angle of 180° and axial actuation force at the other end deforms the tube. Delicately designed and optimized steerable section and fully compliant section enable the soft manipulator high dexterity and stiffness. The basic kinetostatics model of a single segment was established on the basis of geometric and statics, and constrained optimization algorithm promotes finding the actuation inputs for a given desired task configuration. In addition, we have specifically built the design theory for the slits patterned on the tube surface, taking both bending angle and stiffness into account. Experiments demonstrate that the proposed robot arm is dexterous and has greater stiffness compared with same-size continuum robots. Furthermore, experiments also showcase the potential in minimally invasive surgery.

Figures (13)

• Figure 1: (a) Dual-segment CATR. (b) A single-segment CATR. It has two hollow thin-walled tubes, and each of them were patterned with dense tenon-mortise slits. They are fixed at the tip. Pushing/pulling the inner tube steers the patterned section to bend downwards/upwards.
• Figure 2: (a) Cross section of the robot arm under pushed and pulled status. (b) Bending parameters of the co-axial tubes. (c) Base rotation transfers bidirectional bending into 3D bending.
• Figure 3: Statics model of the tubes. The inner tube is only activated by actuation force and the distributed load $q$ from the outer tube. Apart from this, the outer tube is also excited by tangent external force $F_{ET}$ and radial external force $F_{ER}$.
• Figure 4: Asymmetrically patterned tube with mortise-tendon slits. (a) 3D sectional view of the mortise-tendon slits. (b) Sectional view. (c) Expanding view of the patterned tube with parameters of the slits. (e) and (f) tenon-mortise status of inner tube and outer tube in upward bending and downward bending conditions.
• Figure 5: Dual-segment CATR. The distal segment passes through the hollow space of the proximal segment, and then the robot arm has totally 6 DoFs.