Continuum Robots: An Overview

Abstract

When thinking of robots, the image that immediately springs to mind is either an android, designed to resemble human beings and mimic their behavior, or an industrial manipulator, for example, a large machine of rigid steel working in an assembly line. However, robotic systems of multiple forms have been developed to carry out the most diverse tasks, with designs that evolved from readily available structures, such as vehicles, or inspired by nature. In the last decade, more and more bioinspired designs have been enabled by advances in computer science, materials, and manufacturing. Among them, continuum robots, inspired by snakes, trunks, and tendrils, are characterized by a compliant backbone capable of continuous bending, whose shape (configuration, i.e., position and orientation along the backbone curve) is controlled by applying loads through onboard "intrinsic" actuators (e.g., pneumatics or hydraulics) or transmission elements (e.g., tendons, rods, or compliant tubes) that are pushed/pulled from an extremity of the backbone ("extrinsic actuation"). These robots have flexible bodies with a high length to cross-section diameter ratio and are uniquely suited to tasks that require the deployment of tools or sensors with a long reach into tortuous and narrow paths. [1] Continuum robots were first developed in the 1960s [2] and rose to prominence in the late 1990s, [3] when they were often called elephant trunk, [4] tentacle/tendril, [5] or flexible [6] manipulators. Whereas other robots were characterized by intrinsic actuation and larger sizes, research on continuum robots first focused on miniaturization for medical applications, [7,8] leading to extrinsic actuation to enable leaner designs. Recently, continuum robots have been developed for a wider range of applications, including manufacturing, aerospace, search and rescue, and nuclear. In such scenarios, the infinite degrees of freedom (DoFs) of these slender robots enable inspection and intervention in areas that cannot be accessed by conventional robots (e.g., tunnels [9] and gas turbines [10] ).An exhaustive literature search (see Appendix) outlines a surging interest in continuum robots, with a 19.6% average annual growth in publications between 2012 and 2021 (continuum robot search on Web of Science). Three main topics can be observed in recent literature surveys, listed in Table 1. DesignTendon-driven and concentric tube robots are predominant in surveys, but they are not the only design solutions. [18] This richer literature can be attributed to intense research effort toward medical and other small-scale applications when compared to larger-scale tasks (e.g., manipulation) where intrinsic actuation is advantageous.

Toward Bionic Arthroscopy: A Comprehensive Perspective of Continuum Robotics Principles and Prototypes for the Inception of Arthroscopic Surgery Robots

“…Reproduced with permission. [ 188 ] Copyright 2023, Wiley: a) following the leader (FTL) navigation. Reproduced with permission.…”

“…Recent research [188] classifies the kinematics of infinite-DoF continuum robot into continuous kinematics, modal kinematics, and discrete kinematics based on the order reduction of system DoF. Continuous kinematics refers to the backbone of the robot being a continuously variable curvature curve, [94,[189][190][191][192] often modeled using Cosserat rod theory.…”

“…The motion planning modes of continuum robots (see Figure 3) can often be divided into "Following the leader (FTL)," "Coiling," and "Circumnutation". [188] The motion pattern of circumnutation imitates the movements of vines and pea plants in nature. [238,239] It is designed to overcome the disadvantages of slender structures with low stiffness and provide motion support.…”

Continuum Robots: From Conventional to Customized Performance Indicators

“…Continuum robots are characterized by backbones capable of continuous, actuatable bending [ 1 , 2 , 3 ]. Due to their structural flexibility, these elongated robots can navigate across complex environments, crawling through narrow and tortuous paths where conventional rigid-link robots cannot operate.…”

“…A wide range of designs have been proposed for continuum robots, varying both in backbone architecture and in actuation principle [ 2 ]. Successful architectures include robots with a single central backbone [ 8 , 9 ] or a segmented backbone with rigid disks connected by compliant joints (e.g., spring-like [ 10 , 11 ] or twin-pivot [ 4 , 12 ] joints), structures made of sliding disks in series [ 5 ], concentric pre-bent superelastic tubes [ 13 , 14 ], and superelastic notched tubes [ 15 ].…”