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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 70.7 mm s−1, 3.3 rad s−1, and 28.7 mm s−1, respectively. The module integrates the power supply, communication, and control system with a small size of 48 mm × 38 mm × 38 mm, 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. [ABSTRACT FROM AUTHOR]

Seafloor landing research is crucial for underwater robots tasked with long-term fixed-point observation missions, particularly those requiring prolonged operations on the seabed. Developing safe and stable landing technology is essential for the success of these missions. This paper introduces a novel underwater robot by establishing its dynamic model and using the arbitrary Lagrangian–Eulerian (ALE) method to conduct a comprehensive study of its deep-sea landing process. Prior to detailed parameter analysis, the ALE algorithm's effectiveness and accuracy were validated through experimental data and simulation results from previous studies. This study examines the penetration depth and force conditions during the landing process by varying factors such as seabed soil properties, landing velocity, and the robot's mass. Findings indicate that seabed soil properties significantly influence penetration depth and pressure, with variations in soil density and strength affecting the robot's landing behavior. In contrast, the robot's mass has a relatively minor effect, suggesting that the choice of structural materials has limited impact on penetration depth and pressure during landing. Additionally, landing velocity was found to significantly affect penetration depth and pressure; higher velocities result in greater penetration depths and pressures. This highlights the importance of controlling landing velocity to minimize impact forces and protect the robot. The results of this study provide theoretical support and data for developing deep-sea landing technology for novel underwater robots and inform the selection of structural materials, ensuring the successful execution of long-term fixed-point observation missions in deep-sea environments. [ABSTRACT FROM AUTHOR]

A hydrodynamic control model is established in attention to coupling relationships among cable, propellers and robot body of a tethered underwater robot system. In this model the governing equations of umbilical cable and the robot are firstly introduced, then supplementary conditions are coupled into the equations to forming the dynamic mathematical model; finally a hybrid control strategy based on feed-forward negative feedback method for the cable and PID rule for the propellers are integrated in the mathematical model for composing the whole hydrodynamic control model. Both the mathematical model and the control algorithms are proved to be effective and reliable through comparing simulation with the experimental data in existed references. Based on the numerical model constructed in this paper, trajectory tracking of a tethered underwater robot system in different motion combinations are numerically simulated through computational fluid dynamics method. In the numerical simulations, finite difference method is used to solving the kinematic parameters of the mathematical model, while finite volume method is applied on calculating the hydrodynamic forces under a hybrid control manipulations. The robot motion in vertical direction is determined primary by feed-forward negative feedback strategy of adjusting the cable length, while the horizontal movement of the robot is controlled mainly through PID algorithm; The hydrodynamic loading on the robot body are influenced by the flow fields around the robot. Article Highlights: Established the coupling equations with considering dynamic behaviors among propellers, umbilical cable and robot body. Discovered the conversion relation which unrelated to objective factors between the rotating speeds of propellers and the corresponding thrusts. Analyzed the changing rules of hydrodynamic loading on the underwater robot under a hybrid control strategy. [ABSTRACT FROM AUTHOR]

To enhance the maneuverability and adaptability of underwater robots, it is essential to improve their perception of the surrounding environment. Inspired by the hair follicle structure of animal whiskers, this paper proposed a liquid metal-based triboelectric whisker sensor(LTWS) by combining liquid metal with triboelectric nanogenerators. This sensor served as a supplement to optical and acoustic perception technologies for underwater robots in turbid water with low visibility, enhancing the robots’ information perception capabilities. The LTWS mainly consisted of carbon fiber whiskers, silicone sheaths, triggers, memory alloy springs, sensing units, and a base. The subtle deflection of the carbon fiber whiskers drove the trigger to approach and squeeze the sensing unit in the corresponding direction, thereby generating an electric signal. The sensing signal of LTWS had a linear relationship with the lateral displacement of the whiskers, and the sensitivity could reach 7.9 mV/mm. The touch frequency had a small impact on the output signal. LTWS enriched the perception methods of underwater robots, providing a new approach to marine information perception.

The research work presents a novel voxel-type soft amphibious robot based on an assembly of origami flexiballs. The geometric and elastic constitutive models of the origami flexiball are theoretically established to elucidate its intricate deformation mechanism. Especially, the zero-energy storage phenomenon and the quasi-zero-stiffness characteristic are revealed to prove that the origami flexiball is suitable for serving as soft robotic components. As a proof of concept, fourteen origami flexiballs are interconnected to form a quadruped robot capable of walking or crawling in both underwater and terrestrial environments, including flat surfaces and sandy terrain. Its adaptability across multiple environments is enhanced by the origami polyhedra-inspired hollow structure, which naturally adjusts to underwater conditions such as hydrostatic pressure and currents, improving stability and performance. Other advantages of the voxel-type soft amphibious quadruped robot include its ease of manufacture using 3D printing with accessible soft elastic materials, ensuring rapid and cost-effective fabrication. We anticipate its potentially versatile applications, including underwater pipeline inspections, offshore maintenance, seabed exploration, ecological monitoring, and marine sample collection. By leveraging metamaterial features embodied in the origami polyhedra, the presented voxel-type soft robot exemplifies an innovative approach to achieving complex functionalities in soft robotics. [ABSTRACT FROM AUTHOR]

The hot compression tests of underwater vehicle metal material TC17 titanium alloy at deformation temperature of 800 ~ 950 °C and strain rate of 0,01 ~ 10 s-1 were carried out by Thermecmaster-Z thermal simulator. The hot deformation behavior of TC17 ferroalloy was studied. The effects of strain rate and deformation temperature on the high temperature forming of TC17 titanium alloy were analyzed. The multiple linear regression constitutive model of TC17 titanium alloy was established. The results show that the flow stress of TC17 alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. The theoretical value of peak stress obtained by the multiple linear regression constitutive model of TC17 alloy is in good agreement with the experimental results, and the correlation is 97,25%. The model has high prediction accuracy. [ABSTRACT FROM AUTHOR]

Traditional underwater rigid robots have some shortcomings that limit their applications in the ocean. In contrast, because of their inherent flexibility, soft robots, which have gained popularity recently, offer greater adaptability, efficiency, and safety than rigid robots. Among them, the soft actuator is the core component to power the soft robot. Here, we propose a class of soft electrohydraulic bending actuators suitable for underwater robots, which realize the bending motion of the actuator by squeezing the working liquid with an electric field. The actuator consists of a silicone rubber film, polydimethylsiloxane (PDMS) films, soft electrodes, silicone oils, an acrylic frame, and a soft flipper. When a square wave voltage is applied, the actuator can generate continuous flapping motions. By mimicking Haliclystus auricula, we designed an underwater robot based on six soft electrohydraulic bending actuators and constructed a mechanical model of the robot. Additionally, a high-voltage square wave circuit board was created to achieve the robot's untethered motions and remote control using a smart phone via WiFi. The test results show that 1 Hz was the robot's ideal driving frequency, and the maximum horizontal swimming speed of the robot was 7.3 mm/s. [ABSTRACT FROM AUTHOR]

Abstract 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 70.7 mm s−1, 3.3 rad s−1, and 28.7 mm s−1, respectively. The module integrates the power supply, communication, and control system with a small size of 48 mm × 38 mm × 38 mm, 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.

Monitoring turtle behavior is a conservation effort to preserve its habitat, and the detection process is a vital initial stage. On the other hand, robotics demands a deep learning network to automatically detect the presence of sea turtles that can operate in real-time. The need for increased model speed in the inference stage has led to many lightweight vision-based detectors. This work proposes a novel turtle detection to localize multiple sea turtles using a deep learning method. A lightweight primary extractor is applied to distinguish crucial features without producing a huge computational. An excited group attention is offered as an enhancement module that can capture essential turtle components in multi-level convolutional patches. A new turtle dataset is proposed that contains lighting, blur, occlusion, and complex background challenges. The evaluation results show that the proposed model performs higher accuracy than other lightweight object detection models. High-efficiency benefits models that can be implemented on low-end devices in terms of real-time data processing speed.

Abstract Based on the principle of light refraction and binocular ranging, the underwater imaging model is obtained. It provides a theoretical basis for underwater camera calibration. In order to meet the requirement of underwater vehicle to identify and distance underwater target, a new underwater vehicle distance measurement system based on semantic segmentation and binocular vision is proposed. The system uses Deeplabv3 + to identify the underwater target captured by the binocular camera and generate the target map, which is then used for binocular ranging. Compared with the binocular ranging using the original drawing, the measurement accuracy of the proposed method has not changed, the measurement speed is increased by 30%, and the error rate is controlled within 5%, which meets the needs of underwater robot operations.

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents the design and analysis of a biomimetic underwater snake-like robot, addressing the main limitations of current underwater robotic systems in terms of maneuverability and adaptability in complex environments. The innovative design incorporates flexible joint modules that significantly enhance the robot's ability to navigate through narrow and irregular terrains, which is a notable limitation in traditional rigidly connected underwater robots. These flexible joints provide increased degrees of freedom and enable the robot to absorb and release energy, ensuring stability even under external impacts, thus extending the operational lifespan of the robot. Finite element analysis demonstrates the flexible joints' superior performance in various underwater conditions, offering a greater range of motion and workspace compared to rigid connections. The results indicate that the robot's modular design, combined with the flexible joint module, leads to improved agility and maneuverability, allowing for precise and intentional operation. The control module, equipped with advanced sensors and a CPU, manages the complex dynamics introduced by the flexible joints, ensuring effective navigation and operation. The specific advantages of this design include the robot's enhanced structural integrity, its ability to conform to irregular surfaces, and its adaptability to environmental variations. The paper concludes with a discussion on the implications of these findings for the future design and operation of underwater serpentine robots, emphasizing the need for a balance between the effects of elastic modulus and workspace to maximize the benefits of flexible joints. [ABSTRACT FROM AUTHOR]

The beaver-like underwater robot can crawl and swim, playing a significant role in the exploration of amphibious environments. The robot's fan-shaped tail offers partial forward propulsion and enhances motion stability. However, a comprehensive method for modeling this tail motion is lacking. This paper introduces a segmented approach to dynamic modeling, building both propulsion and lift models for the robot's beaver-like tail. The approach integrates hydrodynamics with material mechanics to formulate a fan-shaped flexible dynamics theory. A performance index is established to quantify the tail's motion performance, offering a theoretical foundation for its evaluation. To validate the dynamic model and assess motion performance under varying swing amplitude coefficients, both simulations and experiments are undertaken. An optimal swing amplitude coefficient of 2 is identified, setting the stage for future developments in robotic motion control. This work may also advance dynamic modeling and analysis in other biomimetic underwater robots. [ABSTRACT FROM AUTHOR]

In certain precision work scenarios, underwater robots require the ability to adhere to surfaces in order to perform tasks effectively. An efficient and stable suction device plays a pivotal role in the functionality of such underwater robots. The vortex suction cup, distinguished by its uncomplicated design, high suction efficiency, and capability for non-contact adhesion, holds significant promise for integration into underwater robotic systems. This paper presents a novel design for a vortex suction cup and investigates its suction force and torque when encountering surfaces with varying curvature radii using Computational Fluid Dynamics (CFD) simulations and experimental testing. These findings offer valuable insights for the development of robots capable of adapting to underwater structures of different dimensions. Results from both experiments and simulations indicate that reducing the curvature radius of the adhered surface results in a decrease in suction force and an increase in torque exerted on the suction cup. As the adhered surface transitions from flat to a curvature radius of 150 mm, the adhesion force of our proposed vortex suction cup decreases by approximately 10%, while the torque increases by approximately 20% to 30%. Consequently, the adhesion efficiency of the suction cup decreases by about 25% to 30%. [ABSTRACT FROM AUTHOR]

Biological fish exhibit a remarkably broad-spectrum visual perception capability. Inspired by the eye arrangement of biological fish, we design a fish-like binocular vision system, thereby endowing underwater bionic robots with an exceptionally broad visual perception capacity. Firstly, based on the design principles of binocular visual field overlap and tangency to streamlined shapes, a fish-like vision system is developed for underwater robots, enabling wide-field underwater perception without a waterproof cover. Secondly, addressing the significant distortion and parallax of the vision system, a visual field stitching algorithm is proposed to merge the binocular fields of view and obtain a complete perception image. Thirdly, an orientation alignment method is proposed that draws scales for yaw and pitch angles in the stitched images to provide a reference for the orientation of objects of interest within the field of view. Finally, underwater experiments evaluate the perception capabilities of the fish-like vision system, confirming the effectiveness of the visual field stitching algorithm and the orientation alignment method. The results show that the constructed vision system, when used underwater, achieves a horizontal field of view of 306.56°. The conducted work advances the visual perception capabilities of underwater robots and presents a novel approach to and insight for fish-inspired visual systems. [ABSTRACT FROM AUTHOR]

Underwater robot has been widely used to carry out a variety of underwater inspection and maintenance operations instead of human beings, in which the adsorption structure is an important unit for the robot to face all kinds of complex slope and elevation, so its reliability is very important. But the existing adsorption structure still has some shortcomings such as weak adsorption, poor adaptability and so on. In order to solve these problems, an adsorption structure of underwater robot based on surface negative pressure adsorption is proposed in this paper. The characteristics of the adsorption structure are analyzed through theoretical research, the adsorption structure is simulated by Ansys finite element simulation, and the effects of key parameters on the adsorption force are analyzed and discussed in detail. The theoretical calculation and simulation results show that the adsorption force produced by the adsorption structure is higher than that produced by the thruster and the plane adsorption structure. When the gap between the adsorption structure and the wall is 8 mm, the maximum adsorption force of the plane adsorption structure can reach 136 N, and the curved surface adsorption structure can produce the adsorption force of 194 N, which is equivalent to more than 4.5 times the thrust of the thruster under the same condition. The physical verification and the application verification of the underwater robot are carried out, and the creeping experiments of the robot are carried out on the vertical wall. The results show that the adsorption structure can further improve the adsorption force and contribute to the climbing and adsorption movement of the underwater robot.

This paper presents the optimal design for a robot capable of effectively collecting floating waste on water surfaces by generating a vortex, eliminating the need for manual collection. The robot features a rotating mechanism submerged beneath the water surface, coupled with a water intake pump. This design generates a vortex that funnels fluid flow into the robot. To robustly optimize the collecting performance of floating waste under various conditions, experimental optimization was conducted using the Taguchi method. The experiments determined that the optimal conditions for suction are achieved when the distance from the water surface to the rotating disk is 60 mm, the angle of the disk is 0°, the rotational speed is 40 rpm, and the internal slope angle is 7.5°. Final validation experiments confirmed that floating debris made of plastic and wood, within a diameter of 330 mm, can be effectively collected even at a water flow speed of 100 mm/s.

The hot compression tests of underwater vehicle metal material TC17 titanium alloy at deformation temperature of 800 ~ 950 °C and strain rate of 0,01 ~ 10 s-1 were carried out by Thermecmaster-Z thermal simulator. The hot deformation behavior of TC17 ferroalloy was studied. The effects of strain rate and deformation temperature on the high temperature forming of TC17 titanium alloy were analyzed. The multiple linear regression constitutive model of TC17 titanium alloy was established. The results show that the flow stress of TC17 alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. The theoretical value of peak stress obtained by the multiple linear regression constitutive model of TC17 alloy is in good agreement with the experimental results, and the correlation is 97,25%. The model has high prediction accuracy.

Underwater robots that imitate aquatic life, such as fish-like robots, have attracted attention for oceanographic studies from the viewpoint of morphological affinity for marine life. The existing studies concerning fish-like robots have primarily focused on the swimming mechanism and locomotive performance, and few studies have been conducted on techniques for self-position estimation and obstacle avoidance despite their indispensability in the autonomous navigation of fish-like robots. Therefore, this study aimed to explore a self-positioning estimation method for robotic fish in an environment where global positioning system (GPS) and pre-defined landmarks are not available. To this end, we first developed a fish-like robot that has a laterally flattened shape, which can mimic the swimming pattern of a fish moving forward by waving a tail fin. Next, we realized the function of simple obstacle avoidance using optical distance sensors for autonomous swimming from a practical perspective. Subsequently, we implemented a real-time swimming-path estimation using the posture derived from the inertial measurement unit (IMU) outputs and the swimming speed measured in advance. Furthermore, a swimming path correction method using a particle filter based on a pre-constructed magnetic map was investigated as an alternative to the GPS correction method. Experiments confirmed the accuracy of the swimming path estimation using the proposed method under various conditions, including obstacle avoidance.

The underwater snake robot is a new type of bio-inspired unmanned underwater vehicle. Because snake robots are made of rigid materials, the utilization of articulated joints in a snake robot reduces the degrees of freedom, increases the probability of collision, and ultimately leads to damage of these rigid materials in the complex underwater environment. To resolve such an inevitable issue, this work proposes an innovative approach to tailor the structural composition of the robot, which consists of four different modules: the head module, control module, thruster module, and soft joint module. Thus, we formulate a rigid–soft unified mathematical model by jointly modeling the two types of modules with large differences in their physical characteristics. The snake robot is also known as a typical redundant drive robot, which can use redundant degrees of freedom to complete the multitask control. This establishes a task-priority control method based on the rigid–soft unified model. Therefore, the effectiveness of the controller can be verified by simulating the trajectory tracking control of both ends of the robot in different situations, with the end position and attitude control as the primary task and the base position control as the secondary task. This simulation scenario primarily covers the following three situations: The first situation is that the base remains fixed, and the end tracks a predetermined trajectory. In this case, the snake robot can imitate an industrial mechanical arm to perform terminal tasks in water, such as grasping. The second case is that while the end is tracking a predetermined trajectory, the base also moves according to the predetermined trajectory. The simulation of this situation is indicative of the movement process (e.g., turning) of the snake robot, enabling obstacle avoidance in spacious waters. In the third case, the attitude control of the robot in a fixed position has been verified through simulation studies. We anticipate that both the base and end of the robot will remain in the same position, and the attitude of the end will move according to a predetermined angle. This situation is to simulate the snake robot for capturing more visual information in a narrow underwater environment. The results revealed that when the base is fixed and the end moves, the average tracking error of the end is 1.41% in the X direction and 1.02% in the Y direction. Similarly, when both ends move simultaneously, the average tracking error of the end is 0.53% in the X direction and 1.64% in the Y direction. Moreover, when the terminal attitude is controlled, the average error of pitch angle is 0.38%, and the average error of yaw angle is 0.14%, which verifies the effectiveness of the controller. Such a beneficial performance can considerably reduce the damage of snake robots in complex underwater treatment by means of improving their swimming efficiency and flexibility.

Nuclear power plants play a pivotal role in the global energy infrastructure, fulfilling a substantial share of the world's energy requirements in a sustainable way. The management of these facilities, especially the handling of spent nuclear fuel (SNF), necessitates meticulous inspections to guarantee operational safety and efficiency. However, the prevailing inspection methodologies lean heavily on human operators, which presents challenges due to the potential hazards of the SNF environment. This study introduces the design of a novel Pre-Batched Inspection Strategy (PBIS) that integrates robotic automation and image processing techniques to bolster the inspection process. This methodology deploys robotics to undertake tasks that could be perilous or time-intensive for humans, while image processing techniques are used for precise identification of SNF targets and regulating the robotic system. The implementation of PBIS holds considerable promise in minimizing inspection time and enhancing worker safety. This paper elaborates on the structure, capabilities, and application of PBIS, underlining its potential implications for the future of nuclear energy inspections.

Seafloor landing research is crucial for underwater robots tasked with long-term fixed-point observation missions, particularly those requiring prolonged operations on the seabed. Developing safe and stable landing technology is essential for the success of these missions. This paper introduces a novel underwater robot by establishing its dynamic model and using the arbitrary Lagrangian–Eulerian (ALE) method to conduct a comprehensive study of its deep-sea landing process. Prior to detailed parameter analysis, the ALE algorithm’s effectiveness and accuracy were validated through experimental data and simulation results from previous studies. This study examines the penetration depth and force conditions during the landing process by varying factors such as seabed soil properties, landing velocity, and the robot’s mass. Findings indicate that seabed soil properties significantly influence penetration depth and pressure, with variations in soil density and strength affecting the robot’s landing behavior. In contrast, the robot’s mass has a relatively minor effect, suggesting that the choice of structural materials has limited impact on penetration depth and pressure during landing. Additionally, landing velocity was found to significantly affect penetration depth and pressure; higher velocities result in greater penetration depths and pressures. This highlights the importance of controlling landing velocity to minimize impact forces and protect the robot. The results of this study provide theoretical support and data for developing deep-sea landing technology for novel underwater robots and inform the selection of structural materials, ensuring the successful execution of long-term fixed-point observation missions in deep-sea environments.

The transfer of stagnant water from the basement floor of the waste treatment building at the Fukushima Daiichi Nuclear Power Station is planned because of the possibility of water flowing out of the building if another tsunami occurs. However, the basement floor is installed with high-dose zeolite sandbags as adsorbents for radioactive materials, which renders their removal challenging. In this study, we conduct a field survey and field reproduction as well as develop a robot that can perform zeolite removal based on the results obtained. In addition, we perform verification tests in a full-scale mock-up test environment and extract issues for application to actual equipment. [ABSTRACT FROM AUTHOR]

Copyright of South China Fisheries Science is the property of South China Fisheries Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fishing nets are dangerous obstacles for an underwater robot whose aim is to reach a goal in unknown underwater environments. This paper proposes how to make the robot reach its goal, while avoiding fishing nets that are detected using the robot's camera sensors. For the detection of underwater nets based on camera measurements of the robot, we can use deep neural networks. Passive camera sensors do not provide the distance information between the robot and a net. Camera sensors only provide the bearing angle of a net, with respect to the robot's camera pose. There may be trailing wires that extend from a net, and the wires can entangle the robot before the robot detects the net. Moreover, light, viewpoint, and sea floor condition can decrease the net detection probability in practice. Therefore, whenever a net is detected by the robot's camera, we make the robot avoid the detected net by moving away from the net abruptly. For moving away from the net, the robot uses the bounding box for the detected net in the camera image. After the robot moves backward for a certain distance, the robot makes a large circular turn to approach the goal, while avoiding the net. A large circular turn is used, since moving close to a net is too dangerous for the robot. As far as we know, our paper is unique in addressing reactive control laws for approaching the goal, while avoiding fishing nets detected using camera sensors. The effectiveness of the proposed net avoidance controls is verified using simulations. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) have become the most common choice for the development of mini- and micro-type soft bio-inspired robots due to their high power-to-weight ratio, ability to be installed and operated in limited space, silent and vibration-free operation, biocompatibility, and corrosion resistance properties. Moreover, SMA spring-type actuators are used for developing different continuum robots, exhibiting high degrees of freedom and flexibility. Spring- or any elastic-material-based antagonistic or biasing force is mostly preferred among all other biasing techniques to generate periodic oscillation of SMA actuator-based robotic body parts. In this model-based study, SMA-based spring-type actuators were used to develop a carangiform-type robotic fishtail. Fin size optimization for the maximization of forward thrust was performed for the developed system by varying different parameters, such as caudal fin size, current through actuators, pulse-width modulation signal (PWM), and operating depth. A caudal fin with a mixed fin pattern between the Lunate and Fork "Lunafork" and a fin area of approximately 5000 mm2 was found to be the most effective for the developed system. The maximum forward thrust developed by this fin was recorded as 40 gmf at an operation depth of 12.5 cm in a body of still water. [ABSTRACT FROM AUTHOR]

In recent years, underwater robotics has become very important because it can be applied to various fields such as underwater exploration, underwater inspection, marine industry, and environmental monitoring. Fin plays an essential role in the movement of underwater robots, providing operation, control, and efficient propulsion. This research aims to design and develop a unique robotic fin for underwater robots to improve their handling and propulsion efficiency. The goal is to improve the power density and propulsion efficiency of underwater survey robots. The study is based on a comprehensive analysis of experience and a performance evaluation. Five types of tail fin models were used in the study. The experimental results showed that the performance of the fin design can be compared with existing configurations under different conditions. The best design parameters will be determined by analyzing the experimental results. The results of this study will contribute to underwater robotics by providing a concept of the principles of fin design and its impact on the performance of robotics. [ABSTRACT FROM AUTHOR]

The research work presents a novel voxel-type soft amphibious robot based on an assembly of origami flexiballs. The geometric and elastic constitutive models of the origami flexiball are theoretically established to elucidate its intricate deformation mechanism. Especially, the zero-energy storage phenomenon and the quasi-zero-stiffness characteristic are revealed to prove that the origami flexiball is suitable for serving as soft robotic components. As a proof of concept, fourteen origami flexiballs are interconnected to form a quadruped robot capable of walking or crawling in both underwater and terrestrial environments, including flat surfaces and sandy terrain. Its adaptability across multiple environments is enhanced by the origami polyhedra-inspired hollow structure, which naturally adjusts to underwater conditions such as hydrostatic pressure and currents, improving stability and performance. Other advantages of the voxel-type soft amphibious quadruped robot include its ease of manufacture using 3D printing with accessible soft elastic materials, ensuring rapid and cost-effective fabrication. We anticipate its potentially versatile applications, including underwater pipeline inspections, offshore maintenance, seabed exploration, ecological monitoring, and marine sample collection. By leveraging metamaterial features embodied in the origami polyhedra, the presented voxel-type soft robot exemplifies an innovative approach to achieving complex functionalities in soft robotics.

Traditional underwater rigid robots have some shortcomings that limit their applications in the ocean. In contrast, because of their inherent flexibility, soft robots, which have gained popularity recently, offer greater adaptability, efficiency, and safety than rigid robots. Among them, the soft actuator is the core component to power the soft robot. Here, we propose a class of soft electrohydraulic bending actuators suitable for underwater robots, which realize the bending motion of the actuator by squeezing the working liquid with an electric field. The actuator consists of a silicone rubber film, polydimethylsiloxane (PDMS) films, soft electrodes, silicone oils, an acrylic frame, and a soft flipper. When a square wave voltage is applied, the actuator can generate continuous flapping motions. By mimicking Haliclystus auricula, we designed an underwater robot based on six soft electrohydraulic bending actuators and constructed a mechanical model of the robot. Additionally, a high-voltage square wave circuit board was created to achieve the robot’s untethered motions and remote control using a smart phone via WiFi. The test results show that 1 Hz was the robot’s ideal driving frequency, and the maximum horizontal swimming speed of the robot was 7.3 mm/s.

At present, the simulation model of heave compensation device is usually highly complex, which is not conductive for intuitive understanding of its dynamic characteristics and performance mechanism. Therefore, this paper focuses on a swing-arm and gas-liquid mixed passive heave compensation (PHC) device that is applicable for launching and recovering of deep-sea heavy-duty underwater robots. The complex compensation process and nonlinear dynamic characteristics of the device are analyzed. By establishing reasonable modeling assumptions to reduce modeling complexity, simplified mathematical models of system dynamics and kinematics are derived, and corresponding numerical simulation software is developed. Model-based stability and dynamic simulation analyses are conducted, and the main factors that may affect the passive compensation performance are identified, including accumulator capacity, initial nitrogen charging pressure and nitrogen pressure after oil filling. By simulating the heave compensation performance of the heave compensation device with different design parameters and system states under the condition of still sea surface and degree-3 sea state, and comparing the main factors that affect compensation performance through simulations, the compensation performance of the PHC device in terms of compensation movement range and sensitivity to variations of umbilical cable tension, and the effectiveness of the algorithm model are verified. Based on the simulation results, some suggestions are proposed to improve the performance of the PHC through adjusting accumulator volume and nitrogen pressure.

The ocean area occupies a large part of the earth’s area, how to use underwater robots to carry out deep-sea exploration tasks has become an urgent problem in the field of marine resources. In this paper, we design a small AUV underwater robot from five aspects: power supply, control motherboard, power, communication, and sensor. Due to the complexity of the underwater environment during deep-sea exploration, the sensors of the underwater robot need to be calibrated to facilitate data collection and acquisition. To acquire and process underwater image data, the robot uses optical and acoustic imaging principles. The bitmap algorithm is employed to construct a multi-sensor fusion model for depth detection, which is then analyzed for application. The underwater robot is basically able to reach the specified position quickly and smoothly according to the set motion, and its underwater robot infiltrating the bitmap algorithm (x-axis time of 89s, y-axis time of 98s, and z-axis time of 99s) is obviously faster than that of the traditional SLAM algorithm in terms of convergence speed. The underwater robot navigates approximately 400 m in advance of the deep-sea probe’s localization, which allows for fast and stable error convergence. This study meets the covertness requirements of underwater robots when performing detection tasks, and can achieve independent and autonomous navigation of underwater robots, which has a good application prospect.

To overcome the difficulty in tracking the trajectory of an inspection robot inside a transformer, this paper proposes a distributed model predictive control method. First, the kinematics and dynamics models of a robot in transformer oil are established based on the Lagrange equation. Then, by using the nonlinear model predictive control method and following the distributed control theory, the motion of a robot in transformer oil is decoupled into five independent subsystems. Based on this, a distributed model predictive control (DMPC) method is then developed. Finally, the simulation results indicate that a robot motion control system based on DMPC achieves high tracking accuracy and robustness with reduced computing complexity, and it provides an effective solution for the motion control of robots in narrow environments. [ABSTRACT FROM AUTHOR]

The motion of rotation is ubiquitous in daily life and industry. Compared with electromagnet motors, smart‐material‐based rotary motors may exhibit more flexibility, robustness, and adaptability. Herein, a lightweight, compact dielectric elastomer actuator (DEA) rotary motor with remarkable performance is reported. The motor is driven by a multilayered, slightly‐prestretched (<10%) dielectric elastomer (DE) composite membrane which consists of low‐loss silicone as the DE layers and single‐walled carbon nanotube as electrodes. When operating at frequencies around its resonance, it achieves a maximum rotating speed of 2,850 rpm (to the best of the authors' knowledge, the fastest among all reported DEA rotary motors so far), torque of 0.655 mN m, and power of 34.7 mW with optimized transmission parameters. To demonstrate the motor's practical application, an off‐the‐shelf air vehicle propeller is driven by the motor, and a lift of 26 mN (1.54 times the DEA membrane's own weight) is obtained. An underwater robot driven by a water propeller is designed and a high speed of 175 mm s−1 (1.58 bl s−1) is obtained. The DEA rotary motor of this work paves a new way for driving agile robots in multidomain operations. [ABSTRACT FROM AUTHOR]

This paper deals with the design of a motion and force control scheme for underwater vehicles, each of which has a manipulator. For a subsea operation that requires a contact between the manipulator's tip (e.g., the hand) and various types of environments, it is desirable that the mechanical impedance of the manipulator is adjusted according to the contact surface. From this point of view, the paper focuses on the design of an impedance control scheme. Several impedance controllers have been developed. Most of them were designed on the assumption that the control capability of the vehicle is the same as that of the manipulator. However, it has been pointed out in the literature that for a real underwater robot, its vehicle control is more challenging than its manipulator control, because the vehicle has much larger inertia, and many more inaccurate position sensors and actuators than the manipulator. In view of this fact, we develop an impedance control scheme for the manipulator under the condition that the vehicle is independently controlled by a motion controller with poor performance. Moreover, we provide the results of simulations for comparing an existing controller with the proposed one. [ABSTRACT FROM AUTHOR]