Bioinspired Continuum Robots with Programmable Stiffness by Harnessing Phase Change Materials

Abstract

are referred to as continuum robots. [1] Compared with traditional robots composed of rigid links and joints, continuum robots featured with both softness and compliance exhibit reduced complexity in interactions with the environment in application scenarios, such as minimally invasive surgery, [2] environment exploration, [3] and safe human-robot interaction. [4] As a promising candidate for constructing safe human-centered robots, continuum robots are shifting the mechanical design of intelligent machines from the sole use of rigid materials toward the use of compliant materials. [5] However, these robots are challenged by the inherent contradiction between softness and load-bearing capacity when dealing with stress application scenarios, since the carrying capacity of compliant materials is much worse than that of rigid materials. [6] Aiming at this inherent challenge in existing continuum robots, a hybrid robotic system that combines both soft and rigid materials may figure out the contradiction between the structural stiffness and shape adaption capability. [7] Tensegrity structures, created by Fuller, may provide a novel paradigm for the continuum robotic design. [8] The combination of rigid components and high softness endows this structure with desirable characteristics found in both classically rigid and Continuum robots offer significant advantages over traditional ones in some specific scenarios, such as urban search and rescue, minimally invasive surgery, and inspection of cluttered environments. However, motions and/or operations of existing continuum robots always suffer from those limitations in varying curvature interaction scenarios because of the homogeneity and singleness of the structural stiffness. Herein, inspired by the mechanism of an elephant trunk for regulating local stiffness, a three-segment continuum robot constructed by tensegrity structure, which relies on a stiffness tunable material, with its Young's modulus switchable between 1.79 and 271.62 MPa to achieve the robotic stiffness programmable characteristics, is proposed. For predicting the robotic configuration with varying stiffness distribution, a mechanical model based on the framework of the finite element method is derived. Theoretical predictions reveal that the curvature of each segment can be regulated by programming stiffness of the smart materials; therefore, the customizable design can offer an effective route for real-time robotic interactions. By evaluating motion characteristics, stiffness performance, and conformal interaction capability, the experimental results demonstrate that the robot can freely regulate the configuration on-demand, which may provide a foundation for the application of continuum robots with programmable stiffness for interacting with unstructured environments.

A Magnetically-Actuated Coiling Soft Robot With Variable Stiffness

“…This, however, is non-trivial and one of the significant challenges to the conceptual development of this design. Potential solutions lie in the areas of fluidic actuation [40], phase changing materials [20], electro-statics [41], magnetorheological fluid [21] and vacuum locking [42] and we intend to explore those options with sufficient potential for miniaturization. Further to this we must also develop a mobile mounting system, such as a manual endoscope, to operate.…”

“…Our design, on the contrary, offers a system which is shape locked prior to actuation and mechanical stiffening during the coiling phase is provided by the magnetic actuation itself. This is a novel stiffener/actuator arrangement with potential for future development using alternative stiffening technologies such as the temperature based bulk material property varying systems in [19] and [20] or the magnetorheological stiffening demonstrated in [21]. Low melting point induced variable stiffness was exploited in [19] to achieve stable high deformation bending (≈270 • ) under magnetic actuation.…”

Synergizing Structural Stiffness Regulation with Compliance Contact Stiffness: Bioinspired Soft Stimuli‐Responsive Materials Design for Soft Machines

“…[ 37 ] To circumvent the challenges of high voltage, Zhang et al combined elastic materials and LMPAs to present an intelligent spring with tunable stiffness and then introduced it into a continuum robot to provide a foundation for the application for interacting with unstructured environments. [ 38 ] Nonetheless, the mechanical properties of LMPAs may be altered due to the reaction with the encapsulant, which may lead to unexpected issues, such as encapsulation deterioration and potential material permeation. [ 39 ] Then, Mattmann et al presented variable‐stiffness robotic catheters which could enhance maneuverability and safety in various medical procedures.…”

Design and Analysis of a Novel Bionic Tensegrity Robotic Fish with a Continuum Body

“…With the pre-stretched elastic cables, the tensegrity system can perform a compliant characteristic. Adding extra wire-driven actuation, some variable stiffness mechanisms have been proposed in building spine structures or robot arms [ 31 , 32 , 33 ]. For example, by actively adjusting a ball-joint constraint between adjacent vertebrae, Zappetti et al proposed a variable stiffness tensegrity spine with three stiffness modes [ 31 ].…”