Single-Actuator Soft Robot for In-Pipe Crawling

Rolling Motion of Bar-Driven Soft Spherical Tensegrity Robot Based on Dodecahedron

Soft spherical tensegrity robots exhibit many desirable properties, including impact resistance and extreme lightweight, which give them strong potential for operation in complex environments such as search and rescue missions and space exploration. However, existing spherical tensegrity robots are still unable to achieve 100% exploration in unknown and complex terrains. In this study, we present a 10-bar soft spherical tensegrity robot based on dodecahedron tensegrity (TR-10) with multiple movement gaits. It can generate a rolling motion by actively changing the length of the internal drive module, and the MATLAB dynamic model is established for simulation. The multi-objective optimization method is used to obtain the driving strategies for various basic gaits of the TR-10. The generated movement paths, formed by combining gaits, can fully cover the map. At the same time, the method for determining the rolling axis is proposed, which can enable the robot to roll to the target point along the optimal path. Finally, we fabricated the TR-10 prototype capable of a wireless-controlled rolling motion. By comparing the simulation and experimental results of the basic gaits and movement paths, the effectiveness of the proposed method is verified. In addition, we also compare it with the classical 6-bar 24-cable tensegrity robot, and the results show that our proposed TR-10 can complete different paths with shorter distances and smaller offsets.

Adaptable cavity exploration: Bioinspired vibration-propelled PufferFace Robot with a morphable body

Robots with adaptive morphology can improve interactions with their environment, allowing adaptive functions without complicated control strategies. Inspired by a pufferfish, this paper introduces PufferFace Robot (PFR), a vibration-propelled soft robot with an adaptive design for exploring cavities using simple locomotion strategies. PFR is particularly useful for inspecting centimeter-scale pipeline systems with varying diameters and shapes, which pose substantial challenges. Although recent soft robots using smart materials offer advantages, difficulties remain in handling different pipe sizes, navigating transitions, and managing fluid flow. PFR's inflatable soft skin is equipped with flexible spikes that create asymmetrical friction under vibrations, propelling the robot forward without feedback control. Its hollow structure allows fluid flow, while a front-mounted camera enhances inspection capabilities. PFR adapts to various pipeline conditions, navigating cavities 1 to 1.5 times its diameter and critical areas such as 90° elbows, T-connectors, and high-curvature sections. In specific scenarios, PFR can generate a propulsive force 20 to 35 times its weight.

Weaving liquid crystal elastomer fiber actuators for multifunctional soft robotics

Inspired by the remarkable adaptability observed in biological organisms, multifunctional soft robotics have emerged as promising systems capable of navigating complex environments. In this study, we present a strategy for weaving fiber soft actuators to overcome the existing limitations in deformation capabilities and complex manufacturing processes. This strategy combines traditional rope artistry with the advanced responsive characteristics of electro-driven liquid crystal elastomer (LCE) fibers, facilitating the efficient creation of multifunctional soft actuators. Leveraging this strategy, we have developed four distinct types of soft actuators: the double twisting weaving actuator (DTWA), the circular four-strand weaving actuator (CFWA), the orthogonal weaving actuator (OWA), and the diagonal weaving actuator (DWA). These weaving fiber soft actuators can be readily assembled in various soft robots, granting multiple functionalities, including surface shape programmability, biomimetic blood pumping inspired by the cardiac muscle, and versatile locomotion modes such as crawling and swimming. Our proposed strategy offers unprecedented opportunities for multifunctional soft robots in performing complex tasks.

Soft, Modular Power for Composing Robots with Embodied Energy

The adaptable, modular structure of muscles, combined with their confluent energy storage allows for numerous architectures found in nature: trunks, tongues, and tentacles to name some more complex ones. To provide an artificial analog to this biological soft muscle, a self-powered, soft hydrostat actuator is presented. As an example of how to use these modules, a worm robot is assembled where the near totality of the body stores electrochemical potential. The robot exhibits an extremely high system energy density (51.3 J g-1), using a redox flow battery motif, with a long theoretical operational range of more than 100 m on a single charge. The innovation lies in the battery pouch, fabricated with a dry-adhesion method, automatically bonding Nafion separators to a silicone-urethane copolymer body. These pouches contain anolyte within a hydrostat pod filled with catholyte, increasing current density per pod. Each pod has a motor and tendon actuator for radial compression and expansion. By linking these self-contained pods in series, the robot worm is created that automatically navigates an enclosed, curved path. This high-capacity soft worm also climbs up and down a vertical pipe, using a two-anchor crawling gait, with an extra payload equivalent to 1.5 times its body weight.

Design and mechanical analysis of a novel modular bionic earthworm robot with upright functionality

With the escalating demand for exploration within confined spaces, bionic design methodologies have attracted considerable attention from researchers, primarily due to the intrinsic limitations of human access to hazardous environments. However, contemporary bionic robots primarily attain linear motion through the axial radial deformation of their body segments, thereby lacking the upright functionality that is characteristic of these organisms. In response to the limitations associated with current bionic earthworm robots concerning upright capability and stiffness modulation, we propose an innovative bionic robot that incorporates upright functionality and programmable stiffness. Initially, we present a bionic robot unit module that is capable of attaining an upright posture. A mechanical model is established in accordance with the principle of minimum potential energy to facilitate various compression and deflection functionalities. Through comprehensive simulation and experimental studies, we validate the model's high precision in predicting compression and deformation behaviors. Furthermore, the effects of varying spring stiffness values (k) on device performance are systematically investigated, thereby enabling tailored stiffness adjustments for each module. This programmability empowers the robot to adapt to a broader spectrum of environmental demands. Ultimately, we construct a multi-module robot and successfully evaluate its upright functionality under diverse compression and deformation conditions. The proposed bionic structure, characterized by its enhanced ease of control and programmable stiffness, exhibits considerable potential for applications in complex and unstructured environments.

Tri-Prism Origami Enabled Soft Modular Actuator for Reconfigurable Robots

Soft actuators hold great potential for applications in surgical operations, robotic manipulation, and prosthetic devices. However, they are limited by their structures, materials, and actuation methods, resulting in disadvantages in output force and dynamic response. This article introduces a soft pneumatic actuator capable of bending based on triangular prism origami. The origami creases are crafted by utilizing fabrics to gain swift response and fatigue-resistant properties. By connecting two actuators in series, combined motions including extension and diversified compound bending can be achieved, facilitating control in complex scenarios. After modularizing the soft actuator via mortise and tenon structures, several actuators can be programmed to execute a variety of intricate tasks by adjusting the timing sequences of their contraction and expansion. We showcase its applications in reconfigurable robots, and the results confirm that such a design is adequate for flexibly performing tasks such as soft gripping, navigational movement, and obstacle avoidance. These findings highlight the significance of our actuator in developing soft robots for versatile tasks.

A Symmetrical Leech-Inspired Soft Crawling Robot Based on Gesture Control

This paper presents a novel soft crawling robot controlled by gesture recognition, aimed at enhancing the operability and adaptability of soft robots through natural human-computer interactions. The Leap Motion sensor is employed to capture hand gesture data, and Unreal Engine is used for gesture recognition. Using the UE4Duino, gesture semantics are transmitted to an Arduino control system, enabling direct control over the robot's movements. For accurate and real-time gesture recognition, we propose a threshold-based method for static gestures and a backpropagation (BP) neural network model for dynamic gestures. In terms of design, the robot utilizes cost-effective thermoplastic polyurethane (TPU) film as the primary pneumatic actuator material. Through a positive and negative pressure switching circuit, the robot's actuators achieve controllable extension and contraction, allowing for basic movements such as linear motion and directional changes. Experimental results demonstrate that the robot can successfully perform diverse motions under gesture control, highlighting the potential of gesture-based interaction in soft robotics.

Design of an Adaptive Fixed-Time Fast Terminal Sliding Mode Controller for Multi-Link Robots Actuated by Pneumatic Artificial Muscles

Pneumatic artificial muscles (PAMs) are flexible actuators that can be contracted or expanded by applying air pressure. They are used in robotics, prosthetics, and other applications requiring flexible and compliant actuation. PAMs are basically designed to mimic the function of biological muscles, providing a high force-to-weight ratio and smooth, lifelike movement. Inflation and deflation of these muscles can be controlled rapidly, allowing for fast actuation. In this work, a continuum mechanics-based model is developed to predict the output parameters of PAMs, like actuation force. Comparison of the model results with experimental data shows that the model efficiently predicts the mechanical behaviour of PAMs. Using the actuation force-air pressure-contraction relation provided by the proposed mechanical model, a dynamic model is derived for a multi-link PAM-actuated robot manipulator. An adaptive fixed-time fast terminal sliding mode control is proposed to track the desired joint position trajectories despite the model uncertainties and external disturbances with unknown magnitude bounds. Furthermore, the performance of the proposed controller is compared with an adaptive backstepping fast terminal sliding mode controller through numerical simulations. The simulations show faster convergence and more precise tracking for the proposed controller.

Small-Scale Soft Terrestrial Robot with Electrically Driven Multi-Modal Locomotion Capability

Small-scale soft robots, despite their potential for adaptability in unknown environments, often encounter performance constraints due to inherent limitations within soft actuators and compact bodies. To address this problem, we proposed a fast-moving soft robot driven by electroactive materials. The robot combines the advantages of dielectric elastomer actuators (DEAs) and shape memory alloy (SMA) spring actuators, enabling its high-performance multi-modal locomotion in a small and lightweight design. Theoretical models were constructed for both DEAs and SMA spring actuators to analyze the performance of the designed robot. The robot's design parameters were optimized based on these models to improve its running and jumping performance. The designed robot has a size of 40 × 45 × 25 mm and a weight of 3.5 g. The robot can achieve a running speed of 91 mm/s, ascend a 9° slope, and execute turning motions via an asymmetrical actuation of SMA spring actuators. The robot also demonstrates high-performance jumping motions with a maximum jumping height of 80 mm and the ability to jump over a 40 mm high obstacle. This work introduces a novel approach to designing small-scale soft terrestrial robots, enhancing their agility and mobility in obstacle-laden environments.

A Rolling Soft Robot Driven by Local Snap-Through Buckling

Previous rolling soft robots have difficulty in balancing the locomotion speed with energy efficiency and have limited terrain adaptability. This work proposes a rolling soft robot driven by local snap-through buckling, which employs the fast response and configuration maintenance of the bistable structure to enhance the locomotion performance of the soft robot. A theory based on bifurcation and the energy principle is established to analyze the rolling mechanism. The influences of loading position and geometric parameters on the rolling performance are investigated and verified experimentally. The soft robot shows good locomotion speed (0.95 body length per second, BL/s) and small energy loss due to the almost unchanged configuration during the rolling process. The soft robot adapts to complex terrains, including a step with the height of 15 mm, a slope with the angle of 18.36°, and a broken bridge with the gap length of 90 mm (0.443 BL). The proposed rolling soft robot not only has good application prospects in land exploration missions and medical applications but also provides inspiration for the development of rolling soft robots.

Upgrading and extending the life cycle of soft robots with in situ free-form liquid three-dimensional printing

Soft robotics hardware, with numerous applications ranging from health care to exploration of unstructured environments, suffers from limited life cycles, which lead to waste generation and poor sustainability. Soft robots combine soft or hybrid components via complex assembly and disassembly workflows, which complicate the repair of broken components, hinder upgradability, and ultimately reduce their life spans. In this work, an advanced extrusion-based additive manufacturing process, in situ free-form liquid three-dimensional printing (iFL3DP), was developed to facilitate functional upgrades and repairs in soft robots. A yield-stress hydrogel-a type of material that can maintain its shape until sufficient stress is applied-was first printed directly onto the robot surface, serving as a support for printing new components. This technique enabled the fabrication of advanced components with seamless integration onto already assembled robots. These components could combine multiple materials with intricate geometries, including overhangs and high-aspect ratio shapes, that are considerably challenging to manufacture and integrate via traditional methods such as casting. This approach was successfully applied to upgrade an existing soft robot by adding three advanced functionalities: whisker-like sensors for tactile feedback, a grasping mechanism, and a multifunctional passive whisker array. This study showcases the easy repairability of features, new and old, substantially extending the robot's life span. This workflow has potential to enhance the sustainable development of soft robots.

3D Printed Magnetic Bionic Robot Inspired by Octopus for Drug Transportation

The octopus has attracted widespread attention owing to its unique underwater movement and its ability to escape with inkjets, which also promoted the development of underwater bionic robots. This study introduces a magnetic octopus robot (MOR) 3D printed with PA6/NdFeB composite material, which has good magnetic responsiveness and rigidity to cope with complex environments. The MOR can roll and rotate through complex terrain and passages because of its eight-claw structure. It also has amphibious locomotion and can pass through narrow gaps of 37.5% of its height by deformation. In addition, the MOR can not only clamp, transport, and release solids but also liquids by adding silicone hollow spheres, which indicates the potential of the MOR to be used in medical applications for transporting solid or liquid drugs. This research will help broaden the application prospects of magnetron robots in the field of medical drug transportation.

A toe-inspired rigid-flexible coupling wheel design method for improving the terrain adaptability of a sewer robot

The human toe, characterized by its rigid-flexible structure comprising hard bones and flexible joints, facilitates adaptive and stable movement across varied terrains. In this paper, we utilized a motion capture system to study the adaptive adjustments of toe joints when encountering obstacles. Inspired by the mechanics of toe joints, we proposed a novel design method for a rigid-flexible coupled wheel. The wheel comprises multiple elements: a rigid skeleton, supporting toes, connecting shafts, torsion springs, soft tendons, and damping pads. The torsion springs connect the rigid frame to the supporting toes, enabling them to adapt to uneven terrains and pipes with different diameters. The design was validated through kinematic and dynamic modeling, rigid-flexible coupled dynamics simulation, and stress analysis. Different stiffness coefficients of torsion springs were compared for optimal wheel design. Then, the wheel was applied to a sewer robot, and its performance was evaluated and compared with a pneumatic rubber tire in various experiments, including movement on flat surfaces, overcoming small obstacles, adaptability tests in different terrains, and active driving force tests in dry and wet pipelines. The results prove that the designed wheel showed better stability and anti-slip properties than conventional tires, making it suitable for diverse applications such as pipeline robots, desert vehicles, and lunar rovers.

Untethered soft actuators for soft standalone robotics

Soft actuators produce the mechanical force needed for the functional movements of soft robots, but they suffer from critical drawbacks since previously reported soft actuators often rely on electrical wires or pneumatic tubes for the power supply, which would limit the potential usage of soft robots in various practical applications. In this article, we review the new types of untethered soft actuators that represent breakthroughs and discuss the future perspective of soft actuators. We discuss the functional materials and innovative strategies that gave rise to untethered soft actuators and deliver our perspective on challenges and opportunities for future-generation soft actuators.

Bioinspired Soft Spine Enables Small-Scale Robotic Rat to Conquer Challenging Environments

For decades, it has been difficult for small-scale legged robots to conquer challenging environments. To solve this problem, we propose the introduction of a bioinspired soft spine into a small-scale legged robot. By capturing the motion mechanism of rat erector spinae muscles and vertebrae, we designed a cable-driven centrally symmetric soft spine under limited volume and integrated it into our previous robotic rat SQuRo. We called this newly updated robot SQuRo-S. Because of the coupling compliant spine bending and leg locomotion, the environmental adaptability of SQuRo-S significantly improved. We conducted a series of experiments on challenging environments to verify the performance of SQuRo-S. The results demonstrated that SQuRo-S crossed an obstacle of 1.07 body height, thereby outperforming most small-scale legged robots. Remarkably, SQuRo-S traversed a narrow space of 0.86 body width. To the best of our knowledge, SQuRo-S is the first quadruped robot of this scale that is capable of traversing a narrow space with a width smaller than its own width. Moreover, SQuRo-S demonstrated stable walking on mud-sand, pipes, and slopes (20°), and resisted strong external impact and repositioned itself in various body postures. This work provides a new paradigm for enhancing the flexibility and adaptability of small-scale legged robots with spine in challenging environments, and can be easily generalized to the design and development of legged robots with spine of different scales.

Reprogrammable, intelligent soft origami LEGO coupling actuation, computation, and sensing

Tightly integrating actuation, computation, and sensing in soft materials allows soft robots to respond autonomously to their environments. However, fusing these capabilities within a single soft module in an efficient, programmable, and compatible way is still a significant challenge. Here, we introduce a strategy for integrating actuation, computation, and sensing capabilities in soft origami. Unified and plug-and-play soft origami modules can be reconfigured into diverse morphologies with specific functions or reprogrammed into a variety of soft logic circuits, similar to LEGO bricks. We built an untethered autonomous soft turtle that is able to sense stimuli, store data, process information, and perform swimming movements. The function multiplexing and signal compatibility of the origami minimize the number of soft devices, thereby reducing the complexity and redundancy of soft robots. Moreover, this origami also exhibits strong damage resistance and high durability. We envision that this work will offer an effective way to readily create on-demand soft robots that can operate in unknown environments.

Design and Motion Simulation of a Soft Robot for Crawling in Pipes

In recent years, soft pipeline robot, as a new concept, is proposed to adapt to tunnel. The soft pipeline robots are made of soft materials such as rubber or silicone. These materials have good elasticity, which enhance the adaptability of the soft pipeline robot. Therefore, the soft pipeline robot has better performance on deformability than rigid robot. However, the structure of tunnel is complex and varied that brought challenges on design structure of soft pipeline robot. In this paper, we propose soft pipeline robot with simple structure and easy fabrication, which can be realized straight, turning motion in a variety of tunnels with different diameters. The soft pipeline robot composed of two types of structure, which are expansion part and deformation part. Front and rear deformation part for bending and position fixation, and middle expansion part for elongation, so the pipeline soft robot can be moved in various structures of tunnels. Moreover, the locomotion ability and adaptability in tunnel are verified by simulating on software. The structure of chamber proposed in this paper can guide the design method of soft pipeline robot.