Aquatic Robots Research Articles

Squid-Inspired Anti-Salt Skin-Like Elastomers With Superhigh Damage Resistance for Aquatic Soft Robots.

Cephalopod skins evolve multiple functions in response to environmental adaptation, encompassing nonlinear mechanoreponse, damage tolerance property, and resistance to seawater. Despite tremendous progress in skin-mimicking materials, the integration of these desirable properties into a single material system remains an ongoing challenge. Here, drawing inspiration from the structure of reflectin proteins in cephalopod skins, a long-term anti-salt elastomer with skin-like nonlinear mechanical properties and extraordinary damage resistance properties is presented. Cation-π interaction is incorporated to induce the geometrically confined nanophases of hydrogen bond domains, resulting in elastomers with exceptional true tensile strength (456.5 ± 68.9MPa) and unprecedently high fracture energy (103.7 ± 45.7kJ m-2). Furthermore, the cation-π interaction effectively protects the hydrogen bond domains from corrosion by high-concentration saline solution. The utilization of the resultant skin-like elastomer has been demonstrated by aquatic soft robotics capable of grasping sharp objects. The combined advantages render the present elastomer highly promising for salt enviroment applications, particularly in addressing the challenges posed by sweat, in vivo, and harsh oceanic environments.

Miniature Modular Reconfigurable Underwater Robot Based on Synthetic Jet.

Modular reconfigurable robots exhibit prominent advantages in the reconnaissance and exploration tasks within unstructured environments for their characteristics of high adaptability and high robustness. However, due to the limitations in locomotion mechanism and integration requirements, the modular design of miniature robots in the aquatic environment encounters significant challenges. Here, a modular strategy based on the synthetic jet principle is proposed, and a modular reconfigurable robot system is developed. Specialized bottom and side jet actuators are designed with vibration motors as excitation sources, and a motion module is developed incorporating the jet actuators to realize three-dimensional agile motion. Its linear, rotational, and ascending motion speeds reach 70.7mms-1, 3.3rads-1, and 28.7mms-1, respectively. The module integrates the power supply, communication, and control system with a small size of 48mm × 38mm × 38mm, which ensures a wireless controllable motion. Then, various configurations of the multi-module robot system are established with corresponding motion schemes, and the experiments with replaceable intermediate modules are further conducted to verify the transportation and image-capturing functions. This work demonstrates the effectiveness of synthetic jet propulsion for aquatic modular reconfigurable robot systems, and it exhibits profound potential in future underwater applications.

Vibration-Induced-Flow Mechanism and Its Application in Water Surface Robot.

Vibration is a common strategy for aquatic organisms to achieve their life activities, especially at the air-water interface. For the locomotion of small creatures, the organs with plate features are often used on water surfaces, which inspires relevant studies about using thin plates for robot propulsions. However, the influence of the general deformations of thin plates on the generated flow fields has not been considered. Here, a comprehensive investigation is conducted about the flow fields that arose by vibrations of thin plates and the potential as locomotion strategies are explored. It is discovered that as thin plates are subjected to vibration excitations on the water surface, the produced flow fields are mainly determined by the vibration shapes, and the influence rules of plate deformations on the flow fields are identified. The main factors producing asymmetric flow fields are analyzed to realize the morphology control of the flow fields. Then, to determine effective locomotion strategies on the water surface, the flow fields stimulated by integrated vibration exciters are explored, and 2 water surface robots are developed consequentially, which exhibit superior motion performance. This work reveals the basic rules of the vibration-induced-flow mechanism by thin plates and establishes new locomotion strategies for aquatic robots.

Revolutionizing Aquatic Robotics: Advanced Biomimetic Strategies for Self‐Powered Mobility Across Water Surfaces

Revolutionizing Aquatic Robotics: Advanced Biomimetic Strategies for Self‐Powered Mobility Across Water Surfaces

WaterPairs: a paired dataset for underwater image enhancement and underwater object detection

Due to its importance in marine engineering and aquatic robotics, underwater image enhancement works as a preprocessing step to improve the performance of high-level vision tasks such as underwater object detection and recognition. Although several studies exhibit that underwater image enhancement algorithms can boost the detection accuracy of detectors, no work has focused on studying the relationship between these two tasks. This is mainly because current underwater datasets lack either bounding box annotations or high-quality reference images, based on which detection accuracy or image quality assessment metrics are calculated. To examine how underwater image enhancement methods affect underwater object detection tasks, we provide a large-scale underwater object detection dataset with both bounding box annotations and high-quality reference images, namely, the WaterPairs dataset. The WaterPairs dataset offers a platform for researchers to comprehensively study the influence of underwater image enhancement algorithms on underwater object detection tasks. We will release our dataset at https://github.com/IanDragon/WaterPairs once this paper is accepted.

Bioinspired Design and Experimental Validation of an Aquatic Snake Robot.

This article presents the design, simulation, and experimental validation of a novel modular aquatic snake robot capable of surface locomotion. The modular structure allows each unit to function independently, facilitating ease of maintenance and adaptability to diverse aquatic environments. Employing the material point method with the moving least squares (MPM-MLS) simulation technique, the robot's dynamic behavior was analyzed, yielding reliable results. The control algorithm, integral to the robot's autonomous navigation, was implemented to enable forward propulsion at high speed, steering, and obstacle detection and avoidance. Extensive testing of the aquatic snake robot was conducted, demonstrating its practical viability. The robot showcased promising swimming capabilities, achieving high speeds and maneuverability. Furthermore, the obstacle detection and avoidance mechanisms were proven effective, showing the robot's ability to navigate through dynamic environments. The presented aquatic snake robot represents an advancement in the field of underwater robotics, offering a modular and versatile solution for tasks ranging from environmental monitoring to search and rescue operations.

4D Printed Non-Euclidean-Plate Jellyfish Inspired Soft Robot in Diverse Organic Solvents.

Soft robots have the potential to assist and complement human exploration of extreme and harsh environments (i.e., organic solvents). However, soft robots with stable performance in diverse organic solvents are not developed yet. In the current research, a non-Euclidean-plate under-liquid soft robot inspired by jellyfish based on phototropic liquid crystal elastomers is fabricated via a 4D-programmable strategy. Specifically, the robot employs a 3D-printed non-Euclidean-plate, designed with Archimedean orientation, which undergoes autonomous deformation to release internal stress when immersed in organic solvents. With the assistance of near-infrared light illumination, the organic solvent inside the robot vaporizes and generates propulsion in the form of bubble streams. The developed NEP-Jelly-inspired soft robot can swim with a high degree of freedom in various organic solvents, for example, N, N-dimethylformamide, N, N-dimethylacetamide, tetrahydrofuran, dichloromethane, and trichloromethane, which is not reported before. Besides bionic jellyfish, various aquatic invertebrate-inspired soft robots can potentially be prepared via a similar 4D-programmable strategy.

Numerical Analysis of a Drop-Shaped Aquatic Robot

Finite-dimensional equations constructed earlier to describe the motion of an aquatic drop-shaped robot due to given rotor oscillations are studied. To study the equations of motion, we use the Poincaré map method, estimates of the Lyapunov exponents, and the parameter continuation method to explore the evolution of asymptotically stable solutions. It is shown that, in addition to the so-called main periodic solution of the equations of motion for which the robot moves in a circle in a natural way, an additional asymptotically stable periodic solution can arise under the influence of highly asymmetric impulsive control. This solution corresponds to the robot’s sideways motion near the circle. It is shown that this additional periodic solution can lose stability according to the Neimark–Sacker scenario, and an attracting torus appears in its vicinity. Thus, a quasiperiodic mode of motion can exist in the phase space of the system. It is shown that quasiperiodic solutions of the equations of motion also correspond to the quasiperiodic motion of the robot in a bounded region along a trajectory of a rather complex shape. Also, strange attractors were found that correspond to the drifting motion of the robot. These modes of motion were found for the first time in the dynamics of the drop-shaped robot.

Light and Magnetism Orchestrating Aquatic Pollutant-Degradation Robots in Programmable Trajectories.

Interfacial floating robots have promising applications in carriers, environmental monitoring, water treatment, and so on. Even though, engineering smart robots with both precisely efficient navigation and elimination of water pollutants in long term remains a challenge, as the superhydrophobicity greatly lowers resistance for aquatic motion while sacrificing chemical reactivity of the surface. Here, a pollutant-removing superhydrophobic robot integrated with well-assembled iron oxide-bismuth sulfide heterojunction composite minerals, which provide both light and magnetic propulsion, and the ability of catalytic degradation, is reported. The motion velocity of the robot reaches up to 51.9mm s-1 within only 300ms of acceleration under the orchestration of light, and brakes rapidly (≈200-300ms) once turn off the light. And magnetism extends the robot to work in broad range of surface tensions in any programmable trajectory. Besides, purification of polluted water is efficiently achieved in situ and the degradation efficiency exhibits eightfold enhancements under the effect of light-triggered photothermal behavior coupled with magnetic induction, overcoming the dilemma of efficient motion with catalytic superhydrophobicity. This strategy developed here provides guidelines for the explorations of high-performance smart devices.

PRIDNet based Image Denoising for Underwater Images

Underwater image enhancement has become a popular research topic due to its importance in aquatic robotics and marine engineering. However, the underwater images frequently experience signal-dependent speckle noise when transmitting and acquiring data, which can limit certain applications such as detection, object tracking. In the recent years, the existing underwater image enhancement algorithms efficiency has been analysed and evaluated on a small number of carefully chosen real-world images or synthetic datasets. As such, it is challenging to predict how these algorithms might function with images acquired in the wild under various circumstances. This paper introduces a new solution for noise removal from underwater images called Pyramid Real Image Noise Removal Network (PRIDNet) with patches.PRIDNet is a three-level network design using image patches. The tests were carried out on a dataset of actual noisy images demonstrate that, in terms of quantitative metrics, our proposed denoising model reduction performs better with the exixting denoisers. We determine the effectiveness and constraints of existing algorithms using benchmark assessments and the suggested model, offering valuable information for further studies on underwater image enhancement.

Locomotory Behavior of Water Striders with Amputated Legs.

The stability of the body during locomotion is a fundamental requirement for walking animals. The mechanisms that coordinate leg movement patterns are even more complex at water-air interfaces. Water striders are agile creatures on the water surface, but they can be vulnerable to leg damage, which can impair their movement. One can assume the presence of certain compensatory biomechanical factors that are involved in the maintenance of postural balance lost after an amputation. Here, we studied changes in load distribution among the legs and assessed the effects of amputation on the locomotory behavior and postural defects that may increase the risk of locomotion failure. Apparently, amputees recover a stable posture by applying leg position modifications (e.g., widening the stance) and by load redistribution to the remaining legs. Water striders showed steering failure after amputation in all cases. Amputations affected locomotion by (1) altering motion features (e.g., shorter swing duration of midlegs), (2) functional constraints on legs, (3) shorter travelled distances, and (4) stronger deviations in the locomotion path. The legs functionally interact with each other, and removal of one leg has detrimental effects on the others. This research may assist the bioinspired design of aquatic robots.

An Aerial–Aquatic Hitchhiking Robot with Remora‐Inspired Tactile Sensors and Thrust Vectoring Units

Hybrid aerial–aquatic robots can operate in both air and water and cross between these two. They can be applied to amphibious observation, maritime search and rescue, and cross‐domain environmental monitoring. Herein, an aerial–aquatic hitchhiking robot is proposed that can fly, swim, and rapidly cross the air–water boundaries (0.16 s) and autonomously attach to surfaces in both air and water. Inspired by the mechanoreceptors of the remora (Echeneis naucrates) disc, the robot's hitchhiking device is equipped with two flexible bioinspired tactile sensors (FBTS) based on a triboelectric nanogenerator for tactile sensing of attachment status. Based on tactile sensing, the robot can perform reattachment after leakage or adhesion failure, enabling it to achieve long‐term adhesion on complex surfaces. The rotor‐based aerial–aquatic robot, which has two thrust vectoring units for underwater locomotion, can maneuver to pitch, yaw, and roll 360° and control precision motion position. The field tests show that the robot can continuously cross the air–water boundary, attach to the rough stone surface, and record video in both air and underwater. This study may shed light on future autonomous robots capable of intelligent navigation, adhesion, and operation in complex aerial–aquatic environments.

An Aerial–Aquatic Robot with Tunable Tilting Motors Capable of Multimode Motion

Aerial–aquatic robots have promising applications due to their ability to operate in air and water with different motion modes. However, challenges such as water/air transition and multimedia movement still limit their development. Inspired by the aerial–aquatic behavior of wild ducks, an aerial–aquatic robot with tunable tilting motors and a delta wing is introduced. The robot can perform multimode motion, including flying in air, swimming on the water surface, transitioning between air and water, and diving underwater. Besides, the buoyancy design enables the robot to float at the air–water interface without consuming energy. Herein, the performance of the robot, including vertical and horizontal cross‐media performance, power consumption, and endurance in various motion modes, is evaluated. The field experiments show that the proposed robot possesses multimode motion and high maneuverability. This study provides a new idea for the structural design of next‐generation practical aerial–aquatic robots.

Serpentine motion of a trimaran robot

An aquatic robot is proposed that moves due to the motion of an internal flywheel. The body of the robot represents a trimaran that consists of a capsule and three floats rigidly attached to it. The floats are submerged into the water and ensure that the capsule is afloat. The horizontal cross-section of each float has the shape of an airfoil. The body moves in a horizontal plane. The rotation axis of the internal flywheel is vertical. The control system makes the flywheel to oscillate, which results in oscillations of the robot body together with the floats. It is known that, when an airfoil oscillates in pitch in fluid, a thrust force is produced. As a result, the center of mass of the body moves along a serpentine trajectory. The goal of the study is to describe the effect of geometrical parameters of the robot and coefficients of the control law on the average speed of propulsion. A quasi-steady model is used to describe the hydrodynamic forces acting upon the trimaran. In order to take into account non-steady effects, added masses are considered. This approach allows for describing the robot dynamics with the ODE system. Numerical simulation of the system behavior is performed. Attracting periodic solutions are found using the relaxation method. Parametric analysis of such solutions is performed. A laboratory model is manufactured, and a series of experiments is performed. It is shown theoretically and experimentally that the speed of propulsion of the robot depends non-monotonically on the control frequency.

Backstepping-Based Tracking Control of Underactuated Aquatic Robots

Increased interest in the use of autonomous aquatic robots in a variety of applications has led to the need for efficient and precise control of these robots. In particular, accurate trajectory control has become of importance in many of these applications. However, the highly nonlinear and underactuated dynamics of many aquatic robots present significant challenges in control. In this work, we propose a trajectory-tracking control approach for a general class of underactuated aquatic robotic systems undergoing planar motion. We demonstrate how a backstepping-based control scheme can be synthesized to ultimately bound three tracking errors (2-D position and orientation), despite the underactuated nature of the system. Via multi-time-scale analysis of singularly perturbed systems, we prove how the control scheme achieves boundedness and convergence of the tracking errors to a neighborhood of the origin. Finally, we implement the proposed scheme on a robotic fish and demonstrate its efficacy via experimental results. This article is complemented with a video: https://youtu.be/7007tUQd3KI.

The role of robots in environmental monitoring

PurposeThe purpose of this paper is to illustrate the growing role of robots in environmental monitoring.Design/methodology/approachFollowing an introduction, this first considers aerial robots for monitoring atmospheric pollution. It then discusses the role of aerial, surface and underwater robots to monitor aquatic environments. Some examples are then provided of the robotic monitoring of the terrestrial environment, and finally, brief conclusions are drawn.FindingsRobots are playing an important role in numerous environmental monitoring applications and have overcome many of the limitations of traditional methodologies. They operate in all media and frequently provide data with enhanced spatial and temporal coverage. In addition to detecting pollution and characterising environmental conditions, they can assist in locating illicit activities. Drones have benefited from the availability of small and lightweight imaging devices and sensors that can detect airborne pollutants and also characterise certain features of aquatic and terrestrial environments. As with other robotic applications, environmental drone imagery is benefiting from the use of AI techniques. Ranging from short-term local deployments to extended-duration oceanic missions, aquatic robots are increasingly being used to monitor and characterise freshwater and marine environments.Originality/valueThis provides a detailed insight into the growing number of ways that robots are being used to monitor the environment.

An aquatic biomimetic butterfly soft robot driven by deformable photo-responsive hydrogel.

Taking inspiration from the locomotor behaviors of a butterfly, we have developed an underwater soft robot that imitates its movements. This biomimetic robot is constructed using a deformable photo-responsive material that exhibits high biological compatibility and impressive deformation capabilities in response to external stimuli. First, we investigate composite materials consisting of poly-N-isopropylacrylamide (PNIPAM) and multi-walled carbon nanotubes (MWCNTs). Then, using photocuring printing technology, we successfully fabricate a biomimetic butterfly soft robot utilizing these composite materials. The robot is driven by visible light, enabling it to achieve periodic wing movement and fly upward at an average speed of 3.63 mm s-1. In addition, the robot achieves additional functionalities such as flying over obstacles and carrying small objects during the ascending flight. These outcomes have a significant impact on the advancement of flexible biomimetic robots and offer valuable insights for the research of biomimetic robots driven by visible light.

Application of a self-propelled autonomous aquatic robot for environmental education

Environmental protection in education poses challenges for both teachers and students due to its multidisciplinary nature, involving data acquisition, transfer, data structuring, virtual environment deployment, database access, and data protection. These complexities hinder the preparation of course assignments, and using simulations and modeling as a substitute for technical performance is not recommended for pedagogical reasons. Employing a mobile robot as a data source offers several advantages. Firstly, the data acquisition process becomes transparent, as sensor readings align with intuitively predictable values based on the robot’s trajectory. Secondly, a coherent data structure is formed, connecting diverse data types such as time stamps, coordinates, and sensor readings (e.g., temperature, air and water quality, lighting, distance). Thirdly, the solution’s applicability for environmental monitoring purposes can be easily demonstrated. This study proposes the development of an environmental monitoring solution that employs a self-propelled robot (driving, floating, flying) to obtain readings of environmental parameters. The proposed project solution in education provides many opportunities in data acquisition, processing, transfer, visualization and opens the field for interpretations.

The Control of an Aquatic Robot by a Periodic Rotation of the Internal Flywheel

This paper presents the design of an aquatic robot actuated by one internal rotor. The robot body has a cylindrical form with a base in the form of a symmetric airfoil with a sharp edge. For this object, equations of motion are presented in the form of Kirchhoff equations for rigid body motion in an ideal fluid, which are supplemented with viscous resistance terms. A prototype of the aquatic robot with an internal rotor is developed. Using this prototype, experimental investigations of motion in a fluid are carried out.

A Hybrid Territorial Aquatic Bionic Soft Robot with Controllable Transition Capability

A Hybrid Territorial Aquatic Bionic Soft Robot with Controllable Transition Capability