A Woodpecker’s Tongue-Inspired, Bendable and Extendable Robot Manipulator With Structural Stiffness

Abstract

Woodpeckers have flexible and extendable tongues that they use to reach their prey through tiny openings in trees and insect burrows. This unique capability of their tongue represents a promising design for a tool for picking up and handling objects in unstructured environments. Although continuum robots can produce dexterous movements because of their few shape constraints, the lack of structural stiffness has restricted their deployment in real-world environments. Inspired by the characteristics of woodpeckers, we designed a robot manipulator that can substantially extend its length and bend its shape in 2D space. This behavior is enabled by a backbone consisting of a chain of rigid joints and two flexible rack gears. The joints increase the payload by structurally supporting the robot. The proposed structure is 4.7 times stronger in vertical bending and 6.2 times stronger in torsion than without rigid links. Feeding the rack gears at the same and different speeds allows the robot to elongate and bend, respectively. We developed a geometric model based on a constant curvature model for motion planning. Experiments show that the robot can follow an arbitrary trajectory at an arbitrary tip angle. Lastly, we showcase various demonstrations, including deployment and storage for the backbone, follow-the-leader (FTL) motion, and whole-arm grasping in the horizontal plane.