Energy efficiency of mobile soft robots

3D-Printed Origami Actuators for a Multianimal-Inspired Soft Robot with Amphibious Locomotion and Tongue Hunting

The field of soft robotics is rapidly evolving, and there is a growing interest in developing soft robots with bioinspired features for use in various applications. This research presented the design and development of 3D-printed origami actuators for a soft robot with amphibious locomotion and tongue hunting capabilities. Two different types of programmable origami actuators were designed and manufactured, namely Z-shaped and twist tower actuators. In addition, two actuator variations were developed based on the Z-shaped actuator, including the pelvic fin and the coiling/uncoiling types. The Z-shaped actuators were used for the rear legs to facilitate the locomotion of the water-like frogs. Meanwhile, the twisted tower actuators were used for the rotation joints in the forelegs and for locomotion on land. The pelvic fin actuator was developed to imitate the land locomotion of the mudskipper, and the coiling/uncoiling actuator was designed for tongue hunting motion. The origami actuators and soft robot prototype were tested through a series of experiments, which showed that the robot was capable of efficiently moving in water and on land and performing tongue hunting motions. Our results demonstrate the effectiveness of these actuators in producing the desired motions and provide insights into the potential of applying 3D-printed origami actuators in the development of soft robots with bioinspired features.

Functional soft robotic composites based on organic photovoltaic and dielectric elastomer actuator

Improving the energy efficiency of robots remains a crucial challenge in soft robotics, with energy harvesting emerging as a promising approach to address it. This study presents a functional soft robotic composite called OPV-DEA, which integrates flexible organic photovoltaic (OPV) and dielectric elastomer actuator (DEA). The composite can simultaneously generate electrostatic bending actuation and harvest energy from external lights. Owing to its simplicity and inherent flexibility, the OPV-DEA is poised to function as a fundamental building block for soft robots. This study aimed to validate this concept by initially establishing the fabrication process of OPV-DEA. Subsequently, experimental samples are fabricated and characterized. The results show that the samples exhibit a voltage-controllable bending actuation of up to 15.6° and harvested power output of 1.35 mW under an incident power irradiance of 11.7 mW/cm2. These performances remain consistent even after 1000 actuation cycles. Finally, to demonstrate the feasibility of soft robotic applications, an untethered swimming robot equipped with two OPV-DEAs is fabricated and tested. The robot demonstrates swimming at a speed of 21.7 mm/s. The power consumption of the robot is dominated by a high-voltage DC-DC converter, with a value approximately 1.5 W. As a result, the on-board OPVs cannot supply the necessary energy during locomotion simultaneously. Instead, they contribute to the overall system by charging a battery used for the controller on board. Nevertheless, these findings suggest that the OPV-DEA could pave the way for the development of an unprecedented range of functional soft robots.

Motorized, untethered soft robots via 3D printed auxetics

Untethered operation remains a fundamental challenge in soft robotics. Soft robotic actuators are generally unable to produce the forces required for carrying essential power and control hardware on-board. Moreover, current untethered soft robots often have low operating times given soft actuators' limited efficiency and lifetime. Here, we 3D print cylindrical handed shearing auxetics (HSAs) from single-cure polyurethane resins for use as scalable, motorized soft robotic actuators for untethered machines. Mechanical characterization of individual HSAs confirms their auxetic behaviors and suitability as actuators. HSA pairs of opposite handedness are assembled to form multi-degree-of-freedom legs for untethered quadrupeds. We explore several leg designs to understand the role of length and auxetic pattern density on overall motion and blocked force generated. Finally, we demonstrate untethered locomotion with two soft robotic quadrupeds. We find that our taller soft robot is capable of walking at 2 body lengths per min (BL min^-1) for 65 min, all while carrying a payload of at least 1.5 kg. We compare our soft robots' capabilities to those of previously reported untethered, terrestrial systems and find that our motorized HSAs lead to the second highest operating time with an above average velocity. We anticipate that these methods will open new avenues for designing untethered soft robots with the robustness, operating times, and payload capacities required for future fundamental investigations in embodied intelligence and adaptive, physical learning.

Energy Harvesting for Robots with Adaptive Morphology

Robots primarily made of soft and elastic materials have potential applications such as traveling in confined spaces due to their adaptive morphology. However, their energy efficiency is still subject to improvement. Although a possible approach to increase efficiency is by harvesting the energy used during their behavioral motion, it is not trivial to do so due to their complex dynamics. This work seeks to pioneer a study that exploits the tight coupling between a robot's adaptive morphology, control, and consequent behaviors to harvest energy and increase energy efficiency. It is hypothesized that since varying the robot's morphology may change the energy use that leads to contrasting behavior and efficiency, harvesting the robot's energy will need to be adapted to its morphology. To verify the hypothesis, we developed a shape-changing robot with an elastic structure that achieves locomotion via vibration controlled by a single motor, such that the complex dynamics of the robot can be characterized through its resonance frequencies. It will be shown that harvesting energy at opportune occasions is more important than maximizing the harvest capacity to increase energy efficiency. We will also show how the robot's shape affects energy use in locomotion and how energy harvesting will feedback additional energy that increases the magnitude and affects the robot's behavior. We conclude with an understanding of the role of the robot's morphology, that is, shape, in using the energy provided to the robot and how the understanding can be used to harvest the robot's energy to increase its efficiency.

Increasing Bending Performance of Soft Actuator by Silicon Rubbers of Multiple Hardness

In this study, a method for fabricating actuators made of various silicone materials is proposed to improve the flexural performance of soft-body actuators. Specifically, the redundant deformation part of the soft actuator was replaced with a material with higher hardness to limit the redundant deformation of the soft actuator. Materials with lower hardness were used to produce the main deformation part of the soft actuator, so that the soft body actuator could perform greater bending under the same air pressure and create a greater bending force. In addition, the fabricated actuator was divided into three regions in this study: the periphery of the chamber, the chamber wall (the main curved part), and the bottom surface of the actuator. The impact on the overall performance of soft-body actuators when using silicone materials with different hardness in these three regions was explored in this study. According to the idea of the multi-hardness silicone structure, an actuator with seven chambers was fabricated, and the performance of the actuator was improved by 90.72% compared with the uniform material actuator.

Fractal-inspired soft deployable structure: a theoretical study

The study of soft deployable structures is an emergent field that is highly correlated with metamaterial design, soft robotics, medical devices, etc. This paper studies a novel two-dimensional (2D) soft deployable structure that has a fractal layout with hierarchically coupled thin walls, which buckles upon actuation and deforms into a "peacock tail" pattern that is over 10 fold its original dimension. Large deflection theory and finite-element (FE) modeling are used to characterize its mechanical performance and to investigate its potential application in multiple fields. Further, 2D FE homogenization is implemented to extend the novel design into an active plane lattice metamaterial, on which parametric studies are carried out to explore its effective stiffness and large strain properties. The results show that, besides excellent deformability, the "peacock tail" soft deployable structure and its lattice metamaterial derivates exhibit intriguing properties such as multi-stiffening, strong anisotropy, zero/negative Poisson's ratio, a unique post-buckling collapse mechanism, etc. Three-dimensional generalization of the fractal compliant system is modeled to elaborate on the practical use of the structures. This paper aims to enrich the spectrum of soft deployable structures, shedding light on the research of novel soft robots, hierarchical structures, and metamaterials.

Becoming Sustainable, The New Frontier in Soft Robotics

The advancement of technology has a profound and far-reaching impact on the society, now penetrating all areas of life. From cradle to grave, one is supported by and depends on a wide range of electronic and robotic appliances, with an ever more intimate integration of the digital and biological spheres. These advances, however, often come at the price of negatively impacting our ecosystem, with growing demands on energy, contributions to greenhouse gas emissions and environmental pollution-from production to improper disposal. Mitigating these adverse effects is among the grand challenges of the society and at the forefront of materials research. The currently emerging forms of soft, biologically inspired electronics and robotics have the unique potential of becoming not only like their natural antitypes in performance and capabilities, but also in terms of their ecological footprint. This review outlines the rise of sustainable materials in soft and bioinspired robotics, targeting all robotic components from actuators to energy storage and electronics. The state-of-the-art in biobased robotics spans flourishing fields and applications ranging from microbots operating in vivo to biohybrid machines and fully biodegradable yet resilient actuators. These first steps initiate the evolution of robotics and guide them into a sustainable future.

Underwater maneuvering of robotic sheets through buoyancy-mediated active flutter

Falling leaves flutter from side to side due to passive and intrinsic fluid-body coupling. Exploiting the dynamics of passive fluttering could lead to fresh perspectives for the locomotion and manipulation of thin, planar objects in fluid environments. Here, we show that the time-varying density distribution within a thin, planar body effectively elicits minimal momentum control to reorient the principal flutter axis and propel itself via directional fluttery motions. We validated the principle by developing a swimming leaf with a soft skin that can modulate local buoyancy distributions for active flutter dynamics. To show generality and field applicability, we demonstrated underwater maneuvering and manipulation of adhesive and oil-skimming sheets for environmental remediation. These findings could inspire future intelligent underwater robots and manipulation schemes.

Fabrication of a Dual Stimuli-Responsive Assorted Film Comprising Magnetic- and Gold-Nanoparticles with a Self-Assembly Protein of α-Synuclein

Development of sensing elements for controllable soft materials is crucial to improve their responsiveness toward remotely provided external stimuli. Magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) have been coassembled into a flexible free-floating 2D film to produce a shape deformable mobile structure in the presence of magnetic field and light irradiation by employing a self-assembly protein of α-synuclein (αS). αS was demonstrated to be essential for the preparation of a multisensory system because the intrinsically disordered protein led to a complete dispersion of MNPs to an average size of 10 nm in aqueous solution, pH-dependent closely packed single layer adsorption of αS-MNPs, and α-helix-mediated free-floating MNP monolayer film formation upon dissolving the underlying polycarbonate substrate with chloroform. As AuNPs were incorporated into the assorted hybrid film in the presence of MNPs, however, the β-sheet component became prominent. By placing the assorted film between a spin-coated thin layer of thermoresponsive P(AAc-co-NIPAAm) hydrogel comprising acrylic acid and N-isopropylacrylamide and a passive layer of silicone elastomer, the resulting triply structure exhibited not only magnet-induced locomotion but also shape deformation due to asymmetric contraction of the sandwiching two layers caused by the heat generated by AuNPs upon near IR irradiation. In fact, two adjoining planar layers of another triply structure were shown to form a three-dimensional lotus flower with the light. This multisensory system is suggested to be further functionalized by modifying the αS molecules and incorporating additional nanoparticles to react to diverse stimuli, which would make the system be utilized in the areas of not only soft robotics but also foldable electronics, high-performance sensors/actuators, and medical/wearable applications.

Unfolding Textile-Based Pneumatic Actuators for Wearable Applications

Textile based pneumatic actuators have recently seen increased development for use in wearable applications thanks to their high strength to weight ratio and range of achievable actuation modalities. However, the design of these textile-based actuators is typically an iterative process due to the complexity of predicting the soft and compliant behavior of the textiles. In this work we investigate the actuation mechanics of a range of physical prototypes of unfolding textile-based actuators to understand and develop an intuition for how the geometric parameters of the actuator affect the moment it generates, enabling more deterministic designs in the future. Under benchtop conditions the actuators were characterized at a range of actuator angles and pressures (0 - 136 kPa), and three distinct performance regimes were observed, which we define as Shearing, Creasing, and Flattening. During Flattening, the effects of both the length and radius of the actuator dominate with maximum moments in excess of 80 Nm being generated, while during Creasing the radius dominates with generated moments scaling with the cube of the radius. Low stiffness spring like behavior is observed in the Shearing regime, which occurs as the actuator approaches its unfolded angle. A piecewise analytical model was also developed and compared to the experimental results within each regime. Finally, a prototype actuator was also integrated into a shoulder assisting wearable robot, and on-body characterization of this robot was performed on five healthy individuals to observe the behavior of the actuators in a wearable application. Results from this characterization highlight that these actuators can generate useful on-body moments (10.74 Nm at 90° actuator angle) but that there are significant reductions compared to bench-top performance, in particular when mostly folded and at higher pressures.

Soft Robots for Ocean Exploration and Offshore Operations: A Perspective

The ocean and human activities related to the sea are under increasing pressure due to climate change, widespread pollution, and growth of the offshore energy sector. Data, in under-sampled regions of the ocean and in the offshore patches where the industrial expansion is taking place, are fundamental to manage successfully a sustainable development and to mitigate climate change. Existing technology cannot cope with the vast and harsh environments that need monitoring and sampling the most. The limiting factors are, among others, the spatial scales of the physical domain, the high pressure, and the strong hydrodynamic perturbations, which require vehicles with a combination of persistent autonomy, augmented efficiency, extreme robustness, and advanced control. In light of the most recent developments in soft robotics technologies, we propose that the use of soft robots may aid in addressing the challenges posed by abyssal and wave-dominated environments. Nevertheless, soft robots also allow for fast and low-cost manufacturing, presenting a new potential problem: marine pollution from ubiquitous soft sampling devices. In this study, the technological and scientific gaps are widely discussed, as they represent the driving factors for the development of soft robotics. Offshore industry supports increasing energy demand and the employment of robots on marine assets is growing. Such expansion needs to be sustained by the knowledge of the oceanic environment, where large remote areas are yet to be explored and adequately sampled. We offer our perspective on the development of sustainable soft systems, indicating the characteristics of the existing soft robots that promote underwater maneuverability, locomotion, and sampling. This perspective encourages an interdisciplinary approach to the design of aquatic soft robots and invites a discussion about the industrial and oceanographic needs that call for their application.

A Novel Tendon-Driven Soft Actuator with Self-Pumping Property

Soft actuators and robotics have been widely researched in recent years mainly due to their compliance to environments and safe interaction with humans. However, the need of tether and low energy efficiency of such actuators/robots has limited their practical applications. This article presents a novel tendon-driven soft actuator concept that has the property of self-pumping, called soft self-pumping actuator (SSPA) in this research. A SSPA is designed by assembling two soft pneumatic actuators (SPAs) face-to-face, whose air chambers are connected by two check valves. Actuation of the SSPA is achieved by tendons that allows precise and untethered control compared with traditional SPAs. The two chambers in the proposed actuators are precharged with air to a desired pressure to enlarge self-stiffness and to facilitate bending. When actuated, one chamber will be compressed and serve as a pump to inject its air into the other chamber, resulting in further bending of the actuator. The airflow involves energy transmission to help the intended actuation, thus improving energy efficiency. In experimental studies, differential chamber air pressure is found to reduce the force in initiating actuator bending. Experimental results have also shown that energy efficiency increase of up to 45% has been achieved compared with the same design but without air transmission. We believe that the proposed concept could lead to more novel designs of controllable and energy saving soft robots.

Digital logic for soft devices

Although soft devices (grippers, actuators, and elementary robots) are rapidly becoming an integral part of the broad field of robotics, autonomy for completely soft devices has only begun to be developed. Adaptation of conventional systems of control to soft devices requires hard valves and electronic controls. This paper describes completely soft pneumatic digital logic gates having a physical scale appropriate for use with current (macroscopic) soft actuators. Each digital logic gate utilizes a single bistable valve-the pneumatic equivalent of a Schmitt trigger-which relies on the snap-through instability of a hemispherical membrane to kink internal tubes and operates with binary high/low input and output pressures. Soft, pneumatic NOT, AND, and OR digital logic gates-which generate known pneumatic outputs as a function of one, or multiple, pneumatic inputs-allow fabrication of digital logic circuits for a set-reset latch, two-bit shift register, leading-edge detector, digital-to-analog converter (DAC), and toggle switch. The DAC and toggle switch, in turn, can control and power a soft actuator (demonstrated using a pneu-net gripper). These macroscale soft digital logic gates are scalable to high volumes of airflow, do not consume power at steady state, and can be reconfigured to achieve multiple functionalities from a single design (including configurations that receive inputs from the environment and from human users). This work represents a step toward a strategy to develop autonomous control-one not involving an electronic interface or hard components-for soft devices.

Elementary Slender Soft Robots Inspired by Skeleton Joint System of Animals

In this article, we demonstrate elementary slender soft robots mimicking the skeleton joint system of animals with excellent locomotion performance and scalability. Inspired from bending characteristics of mammal joints, the soft joint, consisting of two Pneu-nets (PNs), one with three chambers and the other with two chambers, was developed. By using simple constraints and connections, the soft joint can be separately controlled by 180° bending and unbending, and exhibits large force output with limited volume and deformation. Then, a skeleton joint-like slender robot was proposed by including a different number of the soft joint and stiff skeleton for different functionalities. This robot exhibits excellent locomotion performance due to the skeleton joint design to achieve large deformation level and proper selection of gait to fully utilize the skeleton joint-like motion, that is, moving 0.5 body length per loading cycle and navigating both continuous terrains, such as a slope, and unprecedented terrains with "discrete" obstacles, such as a wall and stairs. Besides, the slender soft robot is scalable in joint and skeleton, and additional tuning joints can be introduced to achieve turning and spinning locomotion. The slender robot presented herein has not only the advantages of simple fabrication, light weight, good adaptability and scalability, and human-friendly interface but also provides insights for future development of mobile soft robots.