Development of a New Multi-cavity Pneumatic-driven Earthworm-like Soft Robot

Interference Morphology of Free-Growing Tendrils and Application of Self-Locking Structures

Organisms can adapt to various complex environments by obtaining optimal morphologies. Plant tendrils evolve an extraordinary and stable spiral morphology in the free-growing stage. By combining apical and asymmetrical growth strategies, the tendrils can adjust their morphology to wrap around and grab different supports. This phenomenon of changing tendril morphology through the movement of growth inspires a thoughtful consideration of the laws of growth that underlie it. In this study, tendril growth is modeled based on the Kirchhoff rod theory to obtain the exact morphological equations. Based on this, the movement patterns of the tendrils are investigated under different growth strategies. It is shown that the self-interference phenomenon appears as the tendril grows, allowing it to hold onto its support more firmly. In addition, a finite element model is constructed using continuum media mechanics and following the finite growth theory to simulate tendril growth. The growth morphology and self-interference phenomenon of tendrils are observed visually. Furthermore, an innovative class of fluid elastic actuators is designed to verify the growth phenomena of tendrils, which can realize the wrapping and locking functions. Several experiments are conducted to measure the end output force and the smallest size that can be clamped, and the output efficiency of the elastic actuator and the optimal working pressure are verified. The results presented in this study could reveal the formation law of free tendril spiral morphology and provide an inspiring idea for the programmability and motion control of bionic soft robots, with promising applications in the fields of underwater rescue and underwater picking.

Nodes for modes: nodal honeycomb metamaterial enables a soft robot with multimodal locomotion

Soft-bodied animals, such as worms and snakes, use many muscles in different ways to traverse unstructured environments and inspire tools for accessing confined spaces. They demonstrate versatility of locomotion which is essential for adaptation to changing terrain conditions. However, replicating such versatility in untethered soft-bodied robots with multimodal locomotion capabilities have been challenging due to complex fabrication processes and limitations of soft body structures to accommodate hardware such as actuators, batteries and circuit boards. Here, we present MetaCrawler, a 3D printed metamaterial soft robot designed for multimodal and omnidirectional locomotion. Our design approach facilitated an easy fabrication process through a discrete assembly of a modular nodal honeycomb lattice with soft and hard components. A crucial benefit of the nodal honeycomb architecture is the ability of its hard components, nodes, to accommodate a distributed actuation system, comprising servomotors, control circuits, and batteries. Enabled by this distributed actuation, MetaCrawler achieves five locomotion modes: peristalsis, sidewinding, sideways translation, turn-in-place, and anguilliform. Demonstrations showcase MetaCrawler's adaptability in confined channel navigation, vertical traversing, and maze exploration. This soft robotic system holds the potential to offer easy-to-fabricate and accessible solutions for multimodal locomotion in applications such as search and rescue, pipeline inspection, and space missions.

Multimodal steerable earthworm-inspired soft robot based on vacuum and positive pressure powered pneumatic actuators

This article presents a multimodal steerable earthworm-inspired soft robot based on vacuum and positive pressure powered pneumatic actuators capable of crawling both inside pipelines and on planar surfaces. The optimized modular vacuum pressure-driven actuator can generate deformation and anchoring motion through a unified structure under low vacuum pressure, giving it significant speed advantages and multi-modal locomotion capabilities. Meanwhile, the positive pressure powered actuator (PPPA) enables the robot to achieve controlled multi-directional and multi-degrees-of-freedom steering, moreover, enhances the consistency of the driving mechanism. The incorporation of front-end pressure sensing enables the robot to autonomously detect and evaluate pressure, facilitating automatic obstacle avoidance through the activation of corresponding turning units of PPPA. In the process of optimizing motion parameters, the overall motion efficiency has been improved by 16.7% by improving the control law. Through adjustments and optimizations of the interval time (cycle time), the robot is able to achieve a speed of 7.16 mm s-1during planar locomotion and 1.94 mm s-1during in-pipe locomotion. Using the developed robot, we conducted a series of turning experiments, including surface obstacle avoidance and cross-plane crawling, which demonstrated its enhanced capability in cross-plane steering and locomotion. Its related speed indicators showcase superior overall performance compared to other developed robots of the same type.

An earthworm-like modular soft robot for locomotion in multi-terrain environments

Robotic locomotion in subterranean environments is still unsolved, and it requires innovative designs and strategies to overcome the challenges of burrowing and moving in unstructured conditions with high pressure and friction at depths of a few centimeters. Inspired by antagonistic muscle contractions and constant volume coelomic chambers observed in earthworms, we designed and developed a modular soft robot based on a peristaltic soft actuator (PSA). The PSA demonstrates two active configurations from a neutral state by switching the input source between positive and negative pressure. PSA generates a longitudinal force for axial penetration and a radial force for anchorage, through bidirectional deformation of the central bellows-like structure, which demonstrates its versatility and ease of control. The performance of PSA depends on the amount and type of fluid confined in an elastomer chamber, generating different forces and displacements. The assembled robot with five PSA modules enabled to perform peristaltic locomotion in different media. The role of friction was also investigated during experimental locomotion tests by attaching passive scales like earthworm setae to the ventral side of the robot. This study proposes a new method for developing a peristaltic earthworm-like soft robot and provides a better understanding of locomotion in different environments.

Classification Predictive Model for Air Leak Detection in Endoworm Enteroscopy System

Current enteroscopy techniques present complications that are intended to be improved with the development of a new semi-automatic device called Endoworm. It consists of two different types of inflatable cavities. For its correct operation, it is essential to detect in real time if the inflatable cavities are malfunctioning (presence of air leakage). Two classification predictive models were obtained, one for each cavity typology, which must discern between the "Right" or "Leak" states. The cavity pressure signals were digitally processed, from which a set of features were extracted and selected. The predictive models were obtained from the features, and a prior classification of the signals between the two possible states was used as input to different supervised machine learning algorithms. The accuracy obtained from the classification predictive model for cavities of the balloon-type was 99.62%, while that of the bellows-type was 100%, representing an encouraging result. Once the models are validated with data generated in animal model tests and subsequently in exploratory clinical tests, their incorporation in the software device will ensure patient safety during small bowel exploration.

A novel soft-rigid wheeled crawling robot with high payload and passing capability

Soft crawling robots have been significantly studied in recent decades. However, moving in amphibious environment, high payload capability, and passing through complex ground have always been challenges for soft crawling robots. For these problems, this article presents an amphibious soft-rigid wheeled crawling robot (SRWCR) consists of a soft-rigid body actuated by two soft pneumatic actuators (SPAs), four wheels, and four annular soft bladders (ASBs) as brakes. By programming the actuation sequences of the two SPAs and four ASBs, SRWCR can achieve two basic modes of locomotion: linear motion and turning. Based on the energy conservation law, we have developed analytical models to interpret the static actuation performance of SPA, including linear and bending deformations. Furthermore, with the help of fast response and waterproof of SPA and ASB, SRWCR can achieve a linear speed of 14.97 mm/s, a turning speed of 5.63°/s, and an underwater locomotion speed of 13 mm/s, which demonstrates the excellent locomotion performance of SRWCR in amphibious environment. In addition, SRWCR can also achieve multiple impressive functions, including carrying a payload of 2 kg at the moving speed of 11.18 mm/s, passing through various complex ground such as the grass ground and sand ground, and so on, obstacle navigation in confined space. Compared with the existing soft crawling robots, with the help of the soft-rigid body and wheeled structure, SRWCR has the best payload and passing capability, which indicates the potential advantage of SRWCR in the design of functional robots.

A herringbone soft pneu-net actuator for enhanced conformal gripping

Advances in material science in recent years have had such a tremendous impact on the field of soft robotics that has fostered the development of many bio-inspired devices. One such device, which has been subject to extensive study in recent times, is soft pneumatic-network (pneu-net) actuators (SPAs). In this study, we present a new SPA structure whose chamber configuration mimics the fish bone (herringbone) structure to facilitate simultaneous bending deformations in both longitudinal and transverse directions. Such as cannot be obtained from the regular pneu-net structure – which bends only lengthwise, the coupled bending curvatures allow for gripping with maximized contact area, a property which facilitates firmness, security, and stability in gripping. Using the corresponding chamber inclination angle of the configuration as key parameter, the combined transverse and longitudinal deformation feature is studied through finite element simulation as well as experiments. Also, the functional behavior of the actuator/gripper prototypes is experimentally investigated using a series of approaches including blocked (or tip) force test, grip strength test, and stability (or sustained grasping force) test. Furthermore, the viability of the said conformal gripping characteristic is demonstrated by subjecting the structure to a couple of gripping tests. This utility-enhancing design approach could really guide into the development of more sophisticated application-custom soft robotic capabilities.

Design and Experiments of Pneumatic Soft Actuators

The soft actuator is made of superelastic material and embedded flexible material. In this paper, a kind of soft tube was designed and used to assemble two kinds of pneumatic soft actuators. The experiment and finite element analysis are used to comprehensively analyze and describe the bending, elongation, and torsion deformation of the soft actuator. The results show that the two soft actuators have the best actuation performance when the inner diameter of the soft tube is 4 mm. In addition, when the twisting pitch of the torsional actuator is 24 mm, its torsional performance is optimized. Finally, a device that can be used in the production line was assembled by utilizing those soft actuators, and some operation tasks were completed. This experiment provides some insights for the development of soft actuators with more complex motions in the future.