Electrohydrodynamic (EHD) pumps made from flexible or stretchable materials are a promising pumping element for fluidically driven soft robots. In most soft robotic systems, EHD pumps are used separately or connected in series with their target components, such as actuators, which can limit design flexibility and complicate implementation. To address this issue, this paper presents an EHD soft actuator that integrates a pump, actuator, and reservoir into a single device. In this design, the EHD pump is implemented as a flexible PCB, which also serves as a strain-limiting layer, enhancing bending actuation. Additionally, the interdigitated electrodes on the flexible PCB generate fringe electric fields, introducing electroadhesion as an unprecedented functionality for EHD-driven soft actuators. Experimental results from the fabricated actuators demonstrate voltage-controllable actuation, achieving a maximum bending angle of 56.0° and a force of 31.0 mN. The actuators are then incorporated into a soft gripper, where electroadhesion enhances the holding force, with a 1.3× increase for a dielectric object and a 2.9× increase for a conductive object. These enhancements are observed in comparison to a control experiment in which gripping is performed using non-electric, fluidic actuation alone. The results validate the successful implementation of the highly integrated, multifunctional EHD soft actuator, highlighting its potential for soft robotic applications.

This paper presents a soft electrohydraulic actuator integrated with electrically controlled adhesion. Soft electrohydraulic actuators are a type of soft actuation technology known for their versatility and promising features, enabling the creation of diverse soft robotic systems. Integrating electroadhesion functionality into this actuation technology is expected to further enhance its versatility by making it multifunctional. In the actuator proposed in this study, electroadhesion is incorporated by modifying a partial domain of the electrode to have an interdigitated shape, which generates not only actuation but also electrostatic attractive forces to nearby objects simultaneously. Additionally, the geometry of the pouch is modified from a rectangular to a non-rectangular shape to stabilize actuated deformation. The experimental results clarified the actuation performance and electroadhesion forces of the proposed actuator, while a 23% improvement in holding force was observed in the form of a gripper, demonstrating the effectiveness of the actuator with intrinsic electroadhesion.

Drones have shown to be useful aerial vehicles for unmanned transport missions such as food and medical supply delivery. This can be leveraged to deliver life-saving nutrition and medicine for people in emergency situations. However, commercial drones can generally only carry 10 %–30 % of their own mass as payload, which limits the amount of food delivery in a single flight. One novel solution to noticeably increase the food-carrying ratio of a drone, is recreating some structures of a drone, such as the wings, with edible materials. We thus propose a drone, which is no longer only a food-transporting aircraft, but itself is partially edible, increasing its food-carrying mass ratio to 50 %, owing to its edible wings. Furthermore, should the edible drone be left behind in the environment after performing its task in an emergency situation, it will be more biodegradable than its non-edible counterpart, leaving less waste in the environment. Here we describe the choice of materials and scalable design of edible wings, and validate the method in a flight-capable prototype that can provide 300 kcal and carry a payload of 80 g of water.

Soft robotics is an emerging technology with excellent application prospects. However, due to the inherent compliance of the materials used to build soft robots, it is extremely complicated to control soft robots accurately. In this paper, we introduce a data-based control framework for solving the soft robot underwater locomotion problem using deep reinforcement learning (DRL). We first built a soft robot that can swim based on the dielectric elastomer actuator (DEA). We then modeled it in a simulation for the purpose of training the neural network and tested the performance of the control framework through real experiments on the robot. The framework includes the following: a simulation method for the soft robot that can be used to collect data for training the neural network, the neural network controller of the swimming robot trained in the simulation environment, and the computer vision method to collect the observation space from the real robot using a camera. We confirmed the effectiveness of the learning method for the soft swimming robot in the simulation environment by allowing the robot to learn how to move from a random initial state to a specific direction. After obtaining the trained neural network through the simulation, we deployed it on the real robot and tested the performance of the control framework. The soft robot successfully achieved the goal of moving in a straight line in disturbed water. The experimental results suggest the potential of using deep reinforcement learning to improve the locomotion ability of mobile soft robots.

This paper presents a method to create fish-like robots with tensegrity systems and describes a prototype modeled on the body shape of the rainbow trout with a length of 400 mm and a mass of 102 g that is driven by a waterproof servomotor. The structure of the tensegrity robot consists of rigid body segments and elastic cables that represent bone/tissue and muscles of fish, respectively. This structural configuration employing the tensegrity class 2 is much simpler than other tensegrity-based underwater robots. It also allows the tuning of the mechanical stiffness, which is often said to be an important factor in fish swimming. In our robot, the body stiffness can be tuned by changing the cross-section of the cables and their pre-stretch ratio. We characterize the robot in terms of body stiffness, swimming speed, and thrust force while varying the body stiffness i.e., the cross-section of the elastic cables. The results show that the body stiffness of the robot can be designed to approximate that of the real fish and modulate its performance characteristics. The measured swimming speed of the robot is 0.23 m/s (0.58 BL/s), which is comparable to other fish robots of the same type. Strouhal number of the robot 0.54 is close to that of the natural counterpart, suggesting that the presented method is an effective engineering approach to realize the swimming characteristics of real fish.

Bio-inspired underwater robots have several benefits compared to traditional underwater vehicles such as agility, efficiency, and environmentally friendly body. However, bio-inspired underwater robots developed so far have a single swimming mode, which may limit their capability to perform different tasks. This paper presents a re-configurable bio-inspired underwater robot that can change the morphology to enable multiple swimming modes: octopus-mode and fish-mode. The robot is 60 cm long and 50 cm wide, weighing 2.1 kg, and consists of a re-configurable body and 8 compliant arms that are actuated independently by waterproof servomotors. In the robot, the octopus-mode is expected to perform unique tasks such as object manipulation and ground locomotion as demonstrated in literature, while the fish-mode is promising to swim faster and efficiently to travel long distance. With this platform, we investigate the effectiveness of adaptive morphology in bio-inspired underwater robots. For this purpose, we evaluated the robot in terms of the cost of transport and the swimming efficiency of both the morphologies. The fish-mode exhibited a lower cost of transport of 2.2 and higher efficiency of 1.2 % compared to the octopus-mode, illustrating the effect of the multiple swimming modes by adaptive morphology.

We present a fully edible pneumatic actuator based on gelatin-glycerol material. The actuator is monolithic, fabricated via a molding process, and measures 90 mm in length, 20 mm in width, and 17 mm in thickness. Thanks to the material mechanical characteristics similar to those of silicone elastomers, the actuator exhibits a bending angle of 170.3 ° and a blocked force of 0.34 N at the applied pressure of 25 kPa. These values are comparable to elastomer based pneumatic actuators. As a validation example, two actuators are integrated to form a gripper capable of handling various objects, highlighting the high performance and applicability of the edible actuator. These edible actuators, combined with other recent edible materials and electronics, could lay the foundation for a new type of edible robots.

Dielectric elastomer actuators (DEAs), a soft actuator technology, hold great promise for biomimetic underwater robots. The high-voltages required to drive DEAs can however make them challenging to use in water. This paper demonstrates a method to create DEA-based biomimetic swimming robots that operate reliably even in conductive liquids. We ensure the insulation of the high-voltage DEA electrodes without degrading actuation performance by laminating silicone layers. A fish and a jellyfish were fabricated and tested in water. The fish robot has a length of 120 mm and a mass of 3.8 g. The jellyfish robot has a 61 mm diameter for a mass of 2.6 g. The measured swimming speeds for a periodic 3 kV drive voltage were ~8 mm/s for the fish robot, and ~1.5 mm/s for the jellyfish robot.

A novel variable stiffness actuator composed of a dielectric elastomer actuator (DEA) and a low-melting-point-alloy (LMPA) embedded silicone substrate is demonstrated. The device which we call variable stiffness dielectric elastomer actuator (VSDEA) enables functional soft robots with a simplified structure, where the DEA generates a bending actuation and the LMPA provides controllable stiffness between soft and rigid states by Joule heating. The entire structure of VSDEA is made of soft silicones with an elastic modulus of less than 1 MPa providing a high compliance when the LMPA is active. The device has the dimension of 40 mm length × 10 mm width × 1 mm thickness, with mass of ~1 g. We characterize VSDEA in terms of the actuation stroke angle, the blocked force, and the reaction force against a forced displacement. The results show the controllable actuation angle and the blocked force up to 23.7 ° and 2.4 mN in the soft state, and 0.6 ° and 2.1 mN in the rigid state. Compared to an actuator without the LMPA, VSDEA exhibits ~90× higher rigidity. We develop a VSDEA gripper where the mass of active parts is ~2 g, which is able to successfully hold an object mass of 11 g, exhibiting the high performance of the actuator.

This paper aims at mobility enhancement of flexible underwater robots. For this purpose, a novel propulsion method utilizing both static and dynamic deformation of a flexible planar structure is proposed. By actuating the planar structure in two dimensions, various propulsive motions can be generated and the realization of various robotic movements can be expected. Two prototypes of such kind of robots with square and circular shape driven by two pieces of piezoelectric fiber composites has been developed. As the experimental results, the movements with multiple DOFs, holonomic and non-holonomic movements have been realized by the robots. The motion mechanism for the movements are discussed by simulation results.

Fish type underwater robots has a lot of possibilities such as good mobility and high efficiency. Most of the fish type robots developed up to now have complicated mechanisms with complicated motion control. It results in that the structure and the movement of robots are different from that of fishes. The purpose of our work is to develop creature-like flexible underwater robots by using piezoelectric fiber composite. Compared with conventional artificial muscular underwater robots, powerful underwater robots with a very simple structure can be composed. This paper describes the development of a flexible underwater robot with caudal fin propulsion, which can generate large propulsive force and move at high speed. Besides, by utilizing the large propulsive force, pitch and roll motions are realized by attaching two pectoral fins to the robot.