Worm-like Robot Research Articles

Origami-Enhanced Mechanical Properties for Worm-Like Robot.

In recent years, the exploration of worm-like robots has garnered much attention for their adaptability in confined environments. However, current designs face challenges in fully utilizing the mechanical properties of structures/materials to replicate the superior performance of real worms. In this article, we propose an approach to address this limitation based on the stacked Miura origami structure, achieving the seamless integration of structural design, mechanical properties, and robotic functionalities, that is, the mechanical properties originate from the geometric design of the origami structure and at the same time serve the locomotion capability of the robot. Three major advantages of our design are: the implementation of origami technology facilitates a more accessible and convenient fabrication process for segmented robotic skin with periodicity and flexibility, as well as robotic bristles with anchoring effect; the utilization of the Poisson's ratio effect for deformation amplification; and the incorporation of localized folding motion for continuous peristaltic locomotion. Utilizing the high geometric designability inherent in origami, our robot demonstrates customizable morphing and quantifiable mechanical properties. Based on the origami worm-like robot prototype, we experimentally verified the effectiveness of the proposed design in realizing the deformation amplification effect and localized folding motion. By comparing this to a conventional worm-like robot with discontinuous deformation, we highlight the merits of these mechanical properties in enhancing the robot's mobility. To sum up, this article showcases a bottom-up approach to robot development, including geometric design, mechanical characterization, and functionality realization, presenting a unique perspective for advancing the development of bioinspired soft robots.

A review of worm-like pipe inspection robots: research, trends and challenges

In recent years, the development of worm-like robots has increased significantly. These robots use peristaltic motion comprised of radial expansion and axial elongation to move leglessly through their environments. Soft worm-like robots have the advantage of conforming to their environment, making them ideal for confined spaces such as pipelines which are essential to societal infrastructure. Pipeline contamination and corrosion can be detrimental and costly and thus regular checking is vital. Some pipes are difficult to access due to size, access restrictions and harmful waste contamination (such as in nuclear power plants). This has led to an increase of research into soft worm-like robots for pipe inspection. This review will analyse the recent progress in this area to assess current robotic capabilities and where work may be further needed to ensure they are applicable to real-world applications.

Dynamic modeling for continuous locomotion of bionic soft worm-like robot

In the nature, worm-like robot can bend its slender body into an arch bridge when it moves, and it will move quickly in this deformation mode to nimbly escape from enemies once encountering danger. Inspired by this locomotion mechanism, a plenty of bionic soft worm-like robots have been devised and studied adopting quasi-static method. Nevertheless, how to describe the stick-slip transition and the continuity of the entire locomotion process of soft worm-like robots is still a challenging problem. To settle the above issue, a simplified curved beam model is developed to depict a type of soft worm-like robot move forward continuously by controlling its initial curvature in this paper. Based on the curved beam model, a novel dynamic modeling method is further proposed to solve stick-slip nonlinear switchover problem of the soft robot. Since the curved beam is divided into finite segments, an angular variable of an arbitrary point is introduced to elaborate the deformed shape of the curved beam, and then the dimensionless discretized equations of motion can be established via theoretical derivation and solved by implicit integration method. Through dynamic simulation and analysis, a continuous forward locomotion and net displacement of the robot can be easily observed, and several laws of the locomotion are uncovered, which reveals the stick-slip dynamic behaviors. Distinguished from the normal quasi-static modeling approach, the law of motion of the soft worm-like robot is clarified from the dynamic point of view, which will provide important reference for structural design and optimization control of similar soft robots.

Omega motion, rolling, and active standing of a worm-inspired robot under the action of the magnetic field

With the rapid development of origami technologies, worm-inspired robots have attracted a great deal of attention due to their flexible locomotion characteristics. In the present work, we have prepared a soft robot inspired by the worms, which can achieve various locomotion patterns under the actuation of magnetic field. First, the origami technique is used to form the backbone of the robot, and two NdFeB discs are adhered on its two ends. Next, the experiments for controlling the Omega motion and rolling of the robot are performed, and the mechanical analyses are given. In the experiments, the Omega locomotion speed and rolling speed can reach ∼5 mm/s and 2π rad/s, respectively. Then, two typical examples on the composite motion, including the Omega motion and rolling, are demonstrated, where the robot can realize the tasks of sweeping objects and obstacle crossing in unstructured environments. We further design a system to mimic the situation when the worm-like robot detects and responds to the dangerous signal, and the power of the electromagnet can be accurately controlled. These findings cast a new light on engineering intelligent robots and devices originating from the inspirations of living creatures.

Tracking Displacement of a Worm-Like Robot With Multiple Sensor Configurations

Tracking Displacement of a Worm-Like Robot With Multiple Sensor Configurations

Evaluation of Spiral Pneumatic Rubber Actuator Using Finite Element Analysis for Radial Transportation

Emerging actuators with various soft materials and a traveling wave motion are frequently discussed. Various configurations have been proposed and their resulting performances investigated, but it remains challenging to realize large strokes. This study presents an experimentally validated nonlinear finite element model to predict the deformation produced by a spiral pneumatic rubber actuator to generate a traveling wave motion. The actuator consists of a membrane mounted on a rubber substrate with three air chambers in a spiral configuration. The sequential deformations of the successive chambers interact with each other and produce radial traveling waves on the membrane surface, driving the objects placed on the actuator. Finite element analysis with ANSYS computer software was used to analyze the elastic movement by considering the influence of different initial structural types. The simulation results indicated an optimal structure with specific ratios. A reasonable correlation was obtained during experimental validation; the predicted displacement values were approximately 17% smaller than the experimental values. Finally, the transportation performance of the prototype was tested, and a velocity of 2.28 mm/s in the desired direction was achieved. We expect that our demonstration will expand the range of applications of the spiral pneumatic rubber actuator to include conveying or worm-like robots.

A worm-snake-inspired metameric robot for multi-modal locomotion: Design, modeling, and unified gait control

Worm-like and snake-like robots have attracted a great deal of research attention due to their slender bodies and excellent mobility. Based on different locomotion mechanisms, worm-like robots are more suited for movement in restricted environments, while snake-like robots excel in fast movements in open spaces but have limited mobility in confined areas. To complement their advantages, this paper presents a new design and prototype of a Worm-Snake-Inspired Metameric (WSIM) robot with multi-modal locomotion capability, which can execute peristaltic planar locomotion by exploiting the contracting of the worm-like modules and serpentine planar locomotion via active swing of the snake-like joints. We also propose a unified gait control framework that unifies the gait signals of worm-like and snake-like locomotion modes by using the parameter vector, and the conditions that need to be satisfied by the control parameters for generating different gaits are derived. This study also takes a major step forward in establishing dynamic models for the worm-like and snake-like locomotion modes, which can effectively predict the robot's locomotion performance, including the average velocity, slope, and radius of the trajectory. Gait experiments and complex scenario locomotion experiments demonstrate that the WSIM robot indeed has multi-modal locomotion capability and is well suited to execute tasks in complex environments including tubes, open areas, and narrow corridors. The findings of this paper would provide a useful basis for the design, modeling, and control of future bioinspired multi-modal robots.

Modular Design of a Polymer‐Bilayer‐Based Mechanically Compliant Worm‐Like Robot (Adv. Mater. 18/2023)

Soft Robotics Wormlike robots can navigate through uneven terrain and constricted spaces, but it has proved difficult to completely avoid rigid components, limiting the compliance of such machines. In article 2210409, Hillel J. Chiel, Roger D. Quinn, Christoph Weder, Kathryn A. Daltorio, and co-workers report an earthworm-inspired robot that is based on soft polymer actuators. The robot moves through peristaltic locomotion and can wiggle itself through small openings.

Modular Design of a Polymer-Bilayer-Based Mechanically Compliant Worm-Like Robot.

Soft earthworm-like robots that exhibit mechanical compliance can, in principle, navigate through uneven terrains and constricted spaces that are inaccessible to traditional legged and wheeled robots. However, unlike the biological originals thatthey mimic, most of the worm-like robots reported to date contain rigid components that limit their compliance, such as electromotors or pressure-driven actuation systems. Here, a mechanically compliant worm-like robot with a fully modular body that is based on soft polymers is reported. The robot is composed of strategically assembled, electrothermally activated polymer bilayer actuators, which are based on a semicrystalline polyurethane with an exceptionally large nonlinear thermal expansion coefficient. The segments are designed on the basis of a modified Timoshenko model, and finite element analysis simulation is used to describe their performance. Upon electrical activation of the segments with basic waveform patterns, the robot can move through repeatable peristaltic locomotion on exceptionally slippery or sticky surfaces and it can be oriented in any direction. The soft body enables the robot to wriggle through openings and tunnels that are much smaller than its cross-section.

A Single-Joint Worm-like Robot Inspired by Geomagnetic Navigation

Inspired by identifying directions through the geomagnetic field for migrating birds, in this work, we proposed and fabricated a single-joint worm-like robot with a centimeter scale, the motion of which could be easily guided by a magnet. The robot consists of a pneumatic deformable bellow and a permanent magnet fixed in the bellow’s head that will generate magnetic force and friction. Firstly, in order to clarify the actuating mechanism, we derived the relationship between the elongation of the bellows and the air pressure through the Yeoh constitutive model, which was utilized to optimize the structural parameters of the bellow. Then the casting method is introduced to fabricate the silicone bellow with a size of 20 mm in diameter and 28 mm in length. The manufacturing error of the bellow was evaluated by 3D laser scanning technology. Thereafter, the robot’s moving posture was analyzed by considering the force and corresponding motion state, and the analysis model was established by mechanics theory. The experimental results show that the worm-like robot’s maximum speed can reach 9.6 mm/s on the cardboard. Meanwhile, it exhibits excellent environmental adaptability that can move in pipelines with a diameter of 21 mm, 32 mm, 40 mm, and 50 mm, and surfaces with different roughness. Moreover, the robot’s motion was successfully guided under the presence of the magnetic field, which shows great potential for pipeline detection applications.

SpringWorm: A Soft Crawling Robot with a Large-Range Omnidirectional Deformable Rectangular Spring for Control Rod Drive Mechanism Inspection.

In this article, a cable-driven elastic backbone worm-like robot (named "SpringWorm") of decimeter-level size is designed, which has high adaptability in crack inspection of the weld between reactor pressure vessel (RPV) and control rod drive mechanisms. The robot consists of a body that adopts a rectangular helix spring backbone driven by four cables and the flexible claws embedded with distributed electromagnets. Combining the omnidirectional deformation of the backbone and the passive deformation adsorption of the claws, the robot can achieve a variety of gaits. Based on the approaches of geometric analysis and transformation matrices of the coordinate frame, a kinematic model of the cable-driven backbone has been established. Moreover, a mechanical model considering the friction between the cable and the backbone has also been established. The top position and the bending angle of the backbone obtained by the theory, simulation, and experiment are in good agreement. In addition, the errors of the driving force between simulation and experimental results are also small. SpringWorm is 670 g, measures 206 × 65 × 75 mm, has a maximum speed of 8.9 mm/s, and has a maximum payload of 1 kg. The robot can climb over 2-cm-tall steps and 4-cm-deep ditches, and climb and turn on the vertical wall, on the pipe with a radius of 31 cm, and on the spherical surface of RPV.

Locomotion of an untethered, worm-inspired soft robot driven by a shape-memory alloy skeleton

Soft, worm-like robots show promise in complex and constrained environments due to their robust, yet simple movement patterns. Although many such robots have been developed, they either rely on tethered power supplies and complex designs or cannot move external loads. To address these issues, we here introduce a novel, maggot-inspired, magnetically driven “mag-bot” that utilizes shape memory alloy-induced, thermoresponsive actuation and surface pattern-induced anisotropic friction to achieve locomotion inspired by fly larvae. This simple, untethered design can carry cargo that weighs up to three times its own weight with only a 17% reduction in speed over unloaded conditions thereby demonstrating, for the first time, how soft, untethered robots may be used to carry loads in controlled environments. Given their small scale and low cost, we expect that these mag-bots may be used in remote, confined spaces for small objects handling or as components in more complex designs.

Obstacle Avoidance Path Planning for Worm-like Robot Using Bézier Curve.

Worm-like robots have demonstrated great potential in navigating through environments requiring body shape deformation. Some examples include navigating within a network of pipes, crawling through rubble for search and rescue operations, and medical applications such as endoscopy and colonoscopy. In this work, we developed path planning optimization techniques and obstacle avoidance algorithms for the peristaltic method of locomotion of worm-like robots. Based on our previous path generation study using a modified rapidly exploring random tree (RRT), we have further introduced the Bézier curve to allow more path optimization flexibility. Using Bézier curves, the path planner can explore more areas and gain more flexibility to make the path smoother. We have calculated the obstacle avoidance limitations during turning tests for a six-segment robot with the developed path planning algorithm. Based on the results of our robot simulation, we determined a safe turning clearance distance with a six-body diameter between the robot and the obstacles. When the clearance is less than this value, additional methods such as backward locomotion may need to be applied for paths with high obstacle offset. Furthermore, for a worm-like robot, the paths of subsequent segments will be slightly different than the path of the head segment. Here, we show that as the number of segments increases, the differences between the head path and tail path increase, necessitating greater lateral clearance margins.

Multiphysics Simulation of Magnetically Actuated Robotic Origami Worms

Multiphysics simulation of magnetically actuated origami robots promises a range of applications such as synthetic data generation, design parameter optimization, predicting the robot's performance, and implementing various control algorithms, but it has rarely been explored. This letter presents a realistic multiphysics simulation of magnetically actuated origami robots with focus on real-time interactions between the origami and magnets. Due to the interaction between multiple magnets, the complex motion dynamics of a worm-like robot are generated and analyzed. We further show the possibility of accurately simulating origami structures made of different materials and permanent magnets of different shapes, sizes, and magnetic strength. The simulation's unknown parameters are determined by conducting similar practical and simulated experiments and comparing their characteristics. Further, we show the close resemblance between the real and simulated behavior of the origami robot.

MagWorm: A Biomimetic Magnet Embedded Worm-Like Soft Robot.

Emerging worm-like soft robots with various soft materials and different actuation mechanism have been frequently discussed. It is very challenging for soft robots in realizing a fast and untethered crawling. In this article, a biomimetic magnet embedded worm-like robot (shorted as "MagWorm") in the size of centimeter level is designed and investigated. The actuation of the MagWorm is achieved by housing permanent magnetic patches in its soft body, which interact with an external moving drive-magnet system. A dynamic model is established, coupling the discrete elastic rod model with magnetic actuation. The driving mechanism is then numerically studied. Quantitative comparisons between the numerical solution and experiment results show reasonable agreement. It is shown that the MagWorm can deform part of its body into a "Ω" shape and generate biomimetic crawling locomotion. The crawling speed of the robot is studied experimentally with different sizes. Some potential applications are also proposed and demonstrated. The MagWorm represents compact and low-cost solutions that use permanent magnets for remote actuation of soft robot and can be continuously operated during long procedures.

Rapidly Exploring Random Tree Algorithm-Based Path Planning for Worm-Like Robot.

Inspired by earthworms, worm-like robots use peristaltic waves to locomote. While there has been research on generating and optimizing the peristalsis wave, path planning for such worm-like robots has not been well explored. In this paper, we evaluate rapidly exploring random tree (RRT) algorithms for path planning in worm-like robots. The kinematics of peristaltic locomotion constrain the potential for turning in a non-holonomic way if slip is avoided. Here we show that adding an elliptical path generating algorithm, especially a two-step enhanced algorithm that searches path both forward and backward simultaneously, can make planning such waves feasible and efficient by reducing required iterations by up around 2 orders of magnitude. With this path planner, it is possible to calculate the number of waves to get to arbitrary combinations of position and orientation in a space. This reveals boundaries in configuration space that can be used to determine whether to continue forward or back-up before maneuvering, as in the worm-like equivalent of parallel parking. The high number of waves required to shift the body laterally by even a single body width suggests that strategies for lateral motion, planning around obstacles and responsive behaviors will be important for future worm-like robots.

Miniaturization of worm-type soft robot actuated by magnetic field

Recently, many studies on bio-mimic soft robots have been reported. Among living organisms, the locomotion of soft-bodied creatures, such as snails, worms and nematodes, have been actively studied. These soft creatures locomote by deforming the muscles of the whole body into waveforms and propagating the waves of the deformation. This locomotion of soft creatures could be applicable to develop a worm-type soft robot, which can move in drain pipes and even in a human body. In this study, we developed worm-like robots that could generate wavy motion under a rotating magnetic field using silicone and magnetic rubber, and investigated their movement characteristics. In addition, based on a deformation experiment of a silicone cantilever with a single magnetic element inside made of the same material as a worm-like robot, we investigated the effect of the size of the worm robot for further miniaturization.

Turning in Worm-Like Robots: The Geometry of Slip Elimination Suggests Nonperiodic Waves.

Inspired by earthworms, soft robots have demonstrated locomotion using segments with coupled length-wise elongation and radial contraction. However, peristaltic turning has primarily been studied empirically. Surface-dependent slip, which results in frictional forces that deform the body segments, makes accurate models challenging and limited to a specific robot and environment. Here, instead of modeling specific surfaces and segments, we take a geometric approach to analyzing the constraints that result from elimination of slip for the general case of peristaltic locomotion. Thus, our abstract two-dimensional model applies to many different mechanical designs (e.g., fluidic actuation, origami, woven mesh). Specifically, we show how turning is limited by segment range of motion, which means that more than one wave will be required to completely reorient the body in an environment where slip is not possible. As a result, to eliminate slip, segments must undergo nonperiodic shape changes. By representing segments as isosceles trapezoids with reasonable ranges of motion, we can determine control waves that in simulation do not require slip. These waves follow from an initial "reach" (i.e., kinematic movement range) of the second segment. A strategy for choosing the second segment reach is proposed based on evaluating long-term turn stability. To demonstrate the value of the approach, we applied the nonperiodic waveform (NPW) to our earthworm-inspired soft robot, Compliant Modular Mesh Worm with Steering (CMMWorm-S). With the NPW, the robot slips less when compared with a naive periodic waveform, where each segment of the robot has the same kinematic reach of each wave, as indicated by the difference between predicted and actual body position over multiple waves. Using an NPW for turning, we observe a decrease in prediction error compared with a naive periodic waveform by 66%. Thus, while our model ignores many factors (inertial dynamics, radial deformation, surface forces), the resulting turn strategies can improve kinematic motion prediction for planning. The theoretical constraints on NPWs that eliminate slip during turning will help robot designers make application-specific design choices about body stiffness, frictional properties, body length, and degrees of freedom.

A novel serial–parallel hybrid worm-like robot with multi-mode undulatory locomotion

Inspired by the morphology characteristics of segmented worms and the combination properties of serial–parallel structures, a novel serial–parallel hybrid worm-like robot with nine degrees of freedom (DOFs) is proposed. This robot is constructed of two symmetrically arranged 3-RPS parallel mechanisms (PMs) with single-DOF expandable platforms. According to the retrograde peristaltic wave that the locomotion mechanism of segmented worms and the kinematics of the robot, four basic gaits of three undulation modes are developed, including start-up adjustment gait and straight-going gait of rectilinear mode, turning gait of lateral undulation mode, and stair-climbing gait of vertical undulation mode. Based on which, the locomotion performance of the robot on four typical terrains including the stair, the slope, the gap, and the narrow passage is discussed. Then the corresponding locomotion controller is designed. Finally, a prototype is manufactured, the experiment results show that the robot can move in an arbitrary given direction for any given distance, and the practical locomotion performance coincides to the theoretical analysis.

Design and Actuation of a Fabric-Based Worm-Like Robot.

Soft-bodied animals, such as earthworms, are capable of contorting their body to squeeze through narrow spaces, create or enlarge burrows, and move on uneven ground. In many applications such as search and rescue, inspection of pipes and medical procedures, it may be useful to have a hollow-bodied robot with skin separating inside and outside. Textiles can be key to such skins. Inspired by earthworms, we developed two new robots: FabricWorm and MiniFabricWorm. We explored the application of fabric in soft robotics and how textile can be integrated along with other structural elements, such as three-dimensional (3D) printed parts, linear springs, and flexible nylon tubes. The structure of FabricWorm consists of one third the number of rigid pieces as compared to its predecessor Compliant Modular Mesh Worm-Steering (CMMWorm-S), while the structure of MiniFabricWorm consists of no rigid components. This article presents the design of such a mesh and its limitations in terms of structural softness. We experimentally measured the stiffness properties of these robots and compared them directly to its predecessors. FabricWorm and MiniFabricWorm are capable of peristaltic locomotion with a maximum speed of 33 cm/min (0.49 body-lengths/min) and 13.8 cm/min (0.25 body-lengths/min), respectively.