Worm-like Robot Research Articles

Body stiffness in orthogonal directions oppositely affects worm-like robot turning and straight-line locomotion

Earthworms locomote using traveling waves of segment contraction and expansion, which when symmetric result in straight-line locomotion and when biased result in turning. The mechanics of the soft body permit a large range of possible body shapes which both comply with the environment and contribute to directed locomotion. Inspired by earthworms, our new platform Compliant Modular Mesh Worm robot with Steering (CMMWorm-S) has been developed to study this type of locomotion. Compared with our previous robots, CMMWorm-S is capable of an entirely new movement (turning) using two actuated degrees of freedom per segment (a total of 12 motors). The modularity of the mesh, composed of 3D printed rigid pieces and flexible tubes, allows for the interchange of components to vary the stiffness of the robot. On this robotic platform, we show that locomotion efficiency is sensitive to body stiffness. In particular, greater bending stiffness improves turning locomotion, whereas greater circumferential stiffness speeds straight-line locomotion. The data presented demonstrate the contribution of each component towards the longitudinal, circumferential and bending stiffness of mesh-based robots. These analyses can help in the development of design criteria useful for future soft robotic peristaltic devices.

Using Voice Coils to Actuate Modular Soft Robots: Wormbot, an Example.

In this study, we present a modular worm-like robot, which utilizes voice coils as a new paradigm in soft robot actuation. Drive electronics are incorporated into the actuators, providing a significant improvement in self-sufficiency when compared with existing soft robot actuation modes such as pneumatics or hydraulics. The body plan of this robot is inspired by the phylum Annelida and consists of three-dimensional printed voice coil actuators, which are connected by flexible silicone membranes. Each electromagnetic actuator engages with its neighbor to compress or extend the membrane of each segment, and the sequence in which they are actuated results in an earthworm-inspired peristaltic motion. We find that a minimum of three segments is required for locomotion, but due to our modular design, robots of any length can be quickly and easily assembled. In addition to actuation, voice coils provide audio input and output capabilities. We demonstrate transmission of data between segments by high-frequency carrier waves and, using a similar mechanism, we note that the passing of power between coupled coils in neighboring modules—or from an external power source—is also possible. Voice coils are a convenient multifunctional alternative to existing soft robot actuators. Their self-contained nature and ability to communicate with each other are ideal for modular robotics, and the additional functionality of sound input/output and power transfer will become increasingly useful as soft robots begin the transition from early proof-of-concept systems toward fully functional and highly integrated robotic systems.

Helical Kirigami-Enabled Centimeter-Scale Worm Robot With Shape-Memory-Alloy Linear Actuators

The wormlike robots are capable of imitating amazing locomotion of slim creatures. This paper presents a novel centimeter-scale worm robot inspired by a kirigami parallel structure with helical motion. The motion characteristics of the kirigami structure are unravelled by analyzing the equivalent kinematic model in terms of screw theory. This reveals that the kirigami parallel structure with three degrees-of-freedom (DOF) motion is capable of implementing both peristalsis and inchworm-type motion. In light of the revealed motion characteristics, a segmented worm robot which is able to imitate contracting motion, bending motion of omega shape and twisting motion in nature is proposed by integrating kirigami parallel structures successively. Following the kinematic and static characteristics of the kirigami structure, actuation models are explored by employing the linear shape-memory-alloy (SMA) coil springs and the complete procedure for determining the geometrical parameters of the SMA coil springs. Actuation phases for the actuation model with two SMA springs are enumerated and with four SMA springs are calculated based on the Burnside's lemma. In this paper, a prototype of the worm robot with three segments is presented together with a paper-made body structure and integrated SMA coil springs. This centimeter-scale prototype of the worm robot is lightweight and can be used in confined environments for detection and inspection. The study presents an interesting approach of integrating SMA actuators in kirigami-enabled parallel structures for the development of compliant and miniaturized robots.

A 3D undulatory locomotion model inspired by C. elegans through DNN approach

In this work, a 3D undulatory locomotion model inspired by Caenorhabditis elegans is constructed. Following the anatomical structure of C. elegans, the body of the model is represented as a multi-joint rigid link system with 12 links. The angle between two consecutive links is determined by the muscle lengths in four quadrants that are controlled by the nervous system. The nervous system of this locomotion model is represented by a dynamic neural network (DNN) that involves three parts: head DNN, central pattern generator (CPG), and body DNN. The head DNN decides turning or not, and CPG produces the sinusoid waves that are transmitted through the body DNN to control the lengths of muscles. The 3D locomotion behavior is achieved by using the DNN to control the muscle lengths, and then using the muscle lengths to control the angles between two consecutive links on both horizontal plane and vertical plane. In this work, the relations between the outputs of DNN and muscle lengths, as well as the muscle lengths and the angles between two consecutive links, are determined. Furthermore, due to the learning capability of DNN, a set of nonlinear functions that are designed to represent the chemotaxis behaviors of C. elegans are learned by the head DNN using Differential Evolution Algorithm. The testing results show good 3D performance of this locomotion model in both forward and backward locomotion, as well as slight turn and Ω turn. Furthermore, this locomotion model performs the chemotaxis behaviors of finding food and avoiding toxin successfully. Finally, quantitative analyses by comparing with the experiment results are provided to verify the realness and effectiveness of this locomotion model, which could serve as a prototype for the worm-like robot.

Analysis of worm-like locomotion

Nature is a storehouse of great ideas, which are mostly so well planned, that engineers can apply them directly via examining, understanding and imitating the natural working principles. Snakes and worms can be found in almost every region of our planet. Their success is mainly based on the simple construction of their body and their robust locomotion technique. Snakes and worms move their body periodically, to generate propulsive force and get forward, using the interaction with the surrounding environment. The aim of this work is the analysis of a particular worm-like locomotion technique through numerical simulations. The worm is modeled by a multibody system containing lumped masses constrained to each other by ideal rigid rods. The periodic motion of the worm body is achieved via the use of an artificial muscle-like actuator system. The results and experiences can be exploited in future work when a worm-like robot will be built for exploration and rescue purposes.

Analysis and Design of One Degree of Freedom Worm Robots for Locomotion on Rigid and Compliant Terrain

Worm-like robots for applications including maintenance of small pipes and medical procedures in biological vessels such as the intestines, urethra, and blood vessels, have been the focus of many studies in the last few decades. The robots must be small, reliable, energy efficient, and capable of carrying cargos such as cameras, biosensors, and drugs. In this study, worm locomotion along rigid and compliant terrain is analyzed, and a novel design of worm-like multicell robots actuated by a single motor is presented. The robots employ a screw-like axis for sequencing and coordination of the cells and clamps. This design allows for significant miniaturization and reduces complexity and cost. The design of the robots and analysis of their dynamics and power efficiency are described. Two earthworm and two inchworm prototypes were built to demonstrate their performance. The robots are capable of moving forward, backward, and vertically and consume low power, which allow them to climb for hundreds of meters using onboard batteries.

Continuous wave peristaltic motion in a robot

We have developed several innovative designs for a new kind of robot that uses a continuous wave of peristalsis for locomotion, the same method that earthworms use, and report on the first completed prototypes. This form of locomotion is particularly effective in constrained spaces, and although the motion has been understood for some time, it has rarely been effectively or accurately implemented in a robotic platform. As an alternative to robots with long segments, we present a technique using a braided mesh exterior to produce smooth waves of motion along the body of a worm-like robot. We also present a new analytical model of this motion and compare predicted robot velocity to a 2D simulation and a working prototype. Because constant-velocity peristaltic waves form due to accelerating and decelerating segments, it has been often assumed that this motion requires strong anisotropic ground friction. However, our analysis shows that with smooth, constant velocity waves, the forces that cause accelerations within the body sum to zero. Instead, transition timing between aerial and ground phases plays a critical role in the amount of slippage, and the final robot speed. The concept is highly scalable, and we present methods of construction at two different scales.

Analysis of Wormlike Robotic Locomotion on Compliant Surfaces

An inherent characteristic of biological vessels and tissues is that they exhibit significant compliance or flexibility, both in the normal and tangential directions. The latter in particular is atypical of standard engineering materials and presents additional challenges for designing robotic mechanisms for navigation inside biological vessels by crawling on the tissue. Several studies aimed at designing and building wormlike robots have been carried out, but little was done on analyzing the interactions between the robots and their flexible environment. In this study, we will analyze the interaction between earthworm robots and biological tissues where contact mechanics is the dominant factor. Specifically, the efficiency of locomotion of earthworm robots is derived as a function of the tangential flexibility, friction coefficients, number of cells in the robot, and external forces.

Design and Control of an IPMC Wormlike Robot

This paper presents an innovative wormlike robot controlled by cellular neural networks (CNNs) and made of an ionic polymer-metal composite (IPMC) self-actuated skeleton. The IPMC actuators, from which it is made of, are new materials that behave similarly to biological muscles. The idea that inspired the work is the possibility of using IPMCs to design autonomous moving structures. CNNs have already demonstrated their powerfulness as new structures for bio-inspired locomotion generation and control. The control scheme for the proposed IPMC moving structure is based on CNNs. The wormlike robot is totally made of IPMCs, and each actuator has to carry its own weight. All the actuators are connected together without using any other additional part, thereby constituting the robot structure itself. Worm locomotion is performed by bending the actuators sequentially from "tail" to "head," imitating the traveling wave observed in real-world undulatory locomotion. The activation signals are generated by a CNN. In the authors' opinion, the proposed strategy represents a promising solution in the field of autonomous and light structures that are capable of reconfiguring and moving in line with spatial-temporal dynamics generated by CNNs.