Multifunctional Soft Stackable Robots by Netting-Rolling-Splicing Pneumatic Artificial Muscles.

Soft robots are increasingly being explored and developed in various settings that demand safe and adaptable interactions between robots and their environments. In addition, soft robots exhibit passive compliant behavior and generate continuous deformations when engaging with the environment. This imposes challenges on achieving active, on-demand interaction force control, especially when feedback force-sensing devices are not available. Consequently, there is a need to explore new model-based force control paradigms for soft robots. In this article, we propose a (quasi-)static force control approach for soft robots based on compliance modeling, avoiding the necessity for feedback control loops or extensive training data collection. The proposed approach can deliver contact force control along three Cartesian axes when the robot is actuated into various configurations. The compliance matrix is derived from the robot configuration, which allows the calculation of desired deflection displacements needed to generate on-demand forces. The resulting force control is achieved by solving inverse kinematics problems based on these deflection displacements. The efficacy of our proposed controller is validated through experiments with both one- and two-segment pneumatic-driven soft continuum robots. The results demonstrate effective static force control performance, with mean control errors below 5% of the desired peak forces.

Earthworms have entirely soft bodies mainly composed of circular and longitudinal muscle bundles but can handle the complexity of unstructured environments with exceptional multifunctionality. Soft robots are naturally appropriate for mimicking soft animal structures thanks to their inherent compliance. Here, we explore the new possibility of using this compliance to coordinate the actuation movements of single-type soft actuators for not only high adaptability but the simultaneous multifunctionality of soft robots. A cross-linked actuator coordination mechanism is proposed and explained with a novel conceptual design of a cross-linked network, characterization of modular coordinated kinematics, and a modular control strategy for multiple functions. We model and analyze the motion patterns for these functions, including grabbing, manipulation, and locomotion. This further enables the combination of simultaneous multi-functions with this very simple actuator network structure. In this way, a soft modular robot is developed with demonstrations of a novel continuous-transportation mode, for which multiple objects could be simultaneously transported in unstructured environments with either mobile manipulation or pick-and-place operation. A comprehensive workflow is presented to elaborate the cross-linked actuator coordination concept, analytical modeling, modular control strategy, experimental validation, and multi-functional applications. Our understanding of actuator coordination inspires new soft robotic designs for wider robotic applications.

Untethered small-scale (from several millimetres down to a few micrometres in all dimensions) robots that can non-invasively access confined, enclosed spaces may enable applications in microfactories such as the construction of tissue scaffolds by robotic assembly, in bioengineering such as single-cell manipulation and biosensing, and in healthcare such as targeted drug delivery and minimally invasive surgery. Existing small-scale robots, however, have very limited mobility because they are unable to negotiate obstacles and changes in texture or material in unstructured environments. Of these small-scale robots, soft robots have greater potential to realize high mobility via multimodal locomotion, because such machines have higher degrees of freedom than their rigid counterparts. Here we demonstrate magneto-elastic soft millimetre-scale robots that can swim inside and on the surface of liquids, climb liquid menisci, roll and walk on solid surfaces, jump over obstacles, and crawl within narrow tunnels. These robots can transit reversibly between different liquid and solid terrains, as well as switch between locomotive modes. They can additionally execute pick-and-place and cargo-release tasks. We also present theoretical models to explain how the robots move. Like the large-scale robots that can be used to study locomotion, these soft small-scale robots could be used to study soft-bodied locomotion produced by small organisms.

Energy in Robotics: An Interdisciplinary Challenge

Flexible discretely-magnetized configurable soft robots via laser-tuned selective transfer printing of anisotropic ferromagnetic cells

There is a considerable demand for legged robots with exploring capabilities such as passing through narrow pathways. Soft robots can provide a solution for such applications. Here, we propose a soft legged mobile robot with bimorph piezoelectric main body and pre-curved piezoelectric legs. We experimentally demonstrate the performance of the soft mobile robot. The mobile robot can move 70% of the body length per second. In addition, we investigate physical mechanisms behind the locomotion of the mobile robot using a numerical simulation. Interestingly, the mobile robot generates an animal-like running motion. We find that the amplitude difference of the legs, depending on the leg activation condition, may affect the performance of the robot. We also confirm that the soft mobile robot can maintain the movement under impulsive shock owing to its flexibility.

In narrow, unstructured underwater environments such as target monitoring and minimally invasive medical procedures, micro soft robots exhibit unique advantages due to their flexible movement capabilities and small size. At the same time, bionic design of a micro soft robot, can significantly improve their swimming performance. However, limited by their small size, these robots are difficult to power internally and usually adopt a wireless power supply design. This study designs and fabricates a magnetically responsive, bionic micro soft robot based on the swimming principle of the cownose ray. The robot is made of a mixture of neodymium iron boron (NdFeB) and polydimethylsiloxane in a certain proportion. Then, a three-dimensional Helmholtz coil is used to generate an oscillating harmonic magnetic field, allowing for swimming experiments on the robot to explore the influence of magnetic field parameters on its swimming performance. The experimental results show that the swimming speed is fastest atB= 5 mT andf= 11 Hz, reaching 5.25 mm s-1, about 0.5 body lengths per second. Additionally, by adjusting the current direction and frequency of the coil, the robot can execute various swimming modes, including straight swimming, turning swimming, and directional swimming. By employing a stepwise adjustment method, the impact of response errors on the robot's trajectory can be effectively reduced. This study demonstrates the feasibility of a magnetically driven micro soft robot, laying the foundation for the application of wirelessly driven robots in underwater narrow spaces.

Dynamic locomotion of a quadruped robot emerges from interaction between the robot body and the terrain. When the robot has a soft body, dynamic locomotion can be realized using a simple controller. This study investigates dynamic turning of a soft quadruped robot by changing the phase difference among the legs of the robot. We develop a soft quadruped robot driven by McKibben pneumatic artificial muscles. The phase difference between the hind and fore legs is fixed whereas that between the left and right legs is changed to enable the robot to turn dynamically. Since the robot legs are soft, the contact pattern between the legs and the terrain can be varied adaptively by simply changing the phase difference. Experimental results demonstrate that changes in the phase difference lead to changes in the contact time of the hind legs, and as a result, the soft robot can turn dynamically.

This paper presents a novel piezoelectric‐driven and sensing soft robot designed to address the lack of intrinsic sensing capabilities in soft robotic systems. While significant progress is made in soft robot locomotion, most designs still rely on external sensors or complex embedded systems for environmental perception, increasing system complexity, weight, and energy consumption. Developing soft robots with integrated sensing functionalities is crucial for enhancing autonomous interaction and detection, particularly in unstructured environments. The proposed robot features a PVDF/Cu‐based piezoelectric flexible actuator and two asymmetrical arc‐shaped legs, fabricated using a simple and cost‐effective process. Finite element simulations and experiments reveal that its motion is influenced by structural dimensions, voltage amplitude, frequency, and waveform. The optimal configuration—11 mm body length, 6 mm rear leg, 4 mm front leg, 200 Vpp, and ≈100.56 Hz resonance frequency—enables slope climbing, obstacle traversal, and load carrying. Beyond locomotion, the robot leverages the inverse piezoelectric effect to sense mechanical wave signals, similar to how spiders detect web vibrations. By analyzing wave amplitudes, it identifies excitation sources, demonstrating potential for structural health monitoring, environmental sensing, and intelligent micro‐robotics.

Bio-inspired soft robotics: Material selection, actuation, and design

Soft robots typically exhibit limited agility due to inherent properties of soft materials. The structural design of soft robots is one of the key elements to improve their mobility. Inspired by the Archimedean spiral geometry in nature, here, a fast‐moving spiral‐shaped soft robot made of a piezoelectric composite with an amorphous piezoelectric vinylidene fluoride film and a layer of copper tape is presented. The soft robot demonstrates a forward locomotion speed of 76 body length per second under the first‐order resonance frequency and a backward locomotion speed of 11.26 body length per second at the third‐order resonance frequency. Moreover, the multitasking capabilities of the soft robot in slope climbing, step jumping, load carrying, and steering are demonstrated. The soft robot can escape from a relatively confined space without external control and human intervention. An untethered robot with a battery and a flexible circuit (a payload of 1.665 g and a total weight of 1.815 g) can move at an absolute speed of 20 mm s−1 (1 body length per second). This study opens a new generic design paradigm for next‐generation fast‐moving soft robots that are applicable for multifunctionality at small scales.

In this paper, we propose a lightweight indestructible soft robot. Soft robots have soft bodies to adapt to various environments. They are expected to be crash‐proof and to be utilized in unpredictable environments. Although many soft robots driven by pneumatic actuators are proposed due to the affinity between soft robots and the air, they require an external large‐scale air pump to be controlled. It limits the applications of the soft robots to isolated environments. To solve the problem, we employed a wire‐type artificial muscle and developed a lightweight, indestructible and soft robot. We conducted some experiments and confirmed the potential of the developed robot. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

SummaryA design and manufacturing method is described for creating a motor tendon–actuated soft foam robot. The method uses a castable, light, and easily compressible open-cell polyurethane foam, producing a structure capable of large (~70% strain) deformations while requiring low torques to operate (<0.2 N·m). The soft robot can change shape, by compressing and folding, allowing for complex locomotion with only two actuators. Achievable motions include forward locomotion at 13 mm/s (4.3% of body length per second), turning at 9◦/s, and end-over-end flipping. Hard components, such as motors, are loosely sutured into cavities after molding. This reduces unwanted stiffening of the soft body. This work is the first demonstration of a soft open-cell foam robot locomoting with motor tendon actuators. The manufacturing method is rapid (~30 min per mold), inexpensive (under $3 per robot for the structural foam), and flexible, and will allow a variety of soft foam robotic devices to be produced.

Bio-inspired robotic structure composed of soft actuation units has attracted increasing research interests in its potential and capacity of complying with unstructured and dynamic environment, as well as providing safe interaction with human; however, this inevitably poses technical challenging to achieve steady, reliable control due to the remarkable non-linearity of its kinematics and dynamics. To resolve this challenge, we propose a novel control framework that can characterize the kinematics of a soft continuum robot through the hyper-elastic Finite-element modeling (FEM). This enables frequent updates of the Jacobian mapping from the user motion input to the end-effector's point of view. Experimental validation has been conducted to show the feasibility of controlling the soft robot for intracavitary path following. This could be the first success to demonstrate the perspectives of achieving stable, accurate and effective manipulation under large change of robot morphology without having to deduce its analytical model. It is anticipated to draw further extensive attention on resolving the bottleneck against the application of FEM, namely its intensive computation.

This study presents the design and experimental evaluation of a bio‐inspired underwater soft snake robot, using two 3D‐printed soft actuators to replicate anguilliform locomotion. The robot's propulsion is driven by a water pump regulated through phase‐controlled displacement signals and voltage gradients, inducing sinusoidal body undulations with increasing amplitude from head to tail. A series of experiments are conducted to investigate the influence of tail material properties, phase shift values, voltage growth rates, and undulation frequency on swimming performance. Results demonstrate a positive correlation between undulation amplitude and propulsion speed, with both speed and efficiency modulated by tail compliance and gait parameters. The highest performance is achieved with a phase offset of 2/3π, a 3D‐printed PLA tail segment, a voltage growth rate of 1.2, and a undulation period T = 6s reaching a peak underwater speed of 4.464 cm s−1 (0.076 body lengths per second). Notably, locomotion speed increased with phase offset up to an optimal threshold, beyond which performance declined. These findings offer new insights into the mechanics of soft‐bodied aquatic locomotion and contribute to the advancement of high‐efficiency soft robotic swimmers for underwater exploration and bio‐inspired engineering.