Robotic Dolphin Research Articles

Hydrodynamics of standing-and-walking on the water surface by dolphins using collaborative movements of the body and fins

To break the application scenario limitations of traditional bionic underwater robots and open up the way of information docking between underwater and water surface, a systematic study was conducted on the cross-medium standing-and-walking (SAW) behavior of dolphins under the collaborative movements of the body, caudal, and pectoral fins. A three-dimensional physical model of the biomimetic dolphin robot was established, a collaborative movement law of the body, caudal, and pectoral fins was proposed, and the SAW behavior under two modes, Homologous and Reverse modes, was realized. The mapping relationship between the robot's kinematic parameters and hydrodynamic performance parameters was analyzed, the respective advantages of the two vertical walking modes were compared, and the SAW mechanism of the two modes was revealed physically with the help of the evolution law of the flow field around the robot. The results show that the biomimetic dolphin robot can realize cross-medium SAW behavior through the collaborative movements of the body, caudal pectoral fins. It is worth noting that the Hom mode has a superior walking speed, which can reach up to 0.27 m/s, an increase in 83.3% compared to the Rev mode under the same conditions, while the Rev mode has better walking stability, with a minimum fluctuation rate of 2.59%, a 30.8% improvement compared to the Hom mode. This research provides a novel idea for enhancing the surface operation capability of traditional biomimetic underwater robots and provides an important fluid mechanics theoretical basis for the design of new generation of cross-medium dolphin robots.

Analysis of a Dual Tendon-Driven Robotic Dolphin Tail: Omnidirectional Motions and Thrust Characteristics

Analysis of a Dual Tendon-Driven Robotic Dolphin Tail: Omnidirectional Motions and Thrust Characteristics

Fault-tolerant heading control for a bionic gliding robotic dolphin with flipper faults

This paper presents a fault-tolerant heading-control method for a bionic gliding robotic dolphin operating in the presence of flipper faults. To achieve both high manoeuvrability and long endurance, a bionic gliding robotic dolphin that integrates the propulsion modes of dolphins and underwater gliders is introduced. The operational conditions of the flippers are considered meticulously, and common fault types that can arise during the gliding process, such as stuck, failure, and efficiency-loss faults, are analysed. These faults can affect the heading capabilities of the gliding robotic dolphin. To ensure normal navigation in the presence of flipper faults, a fault-tolerant heading control method is devised for the gliding robotic dolphin. This method applies backstepping sliding control to establish control laws based on a dynamic model. Subsequently, a flipper angle solver is designed to convert the controller outputs into deflection angles for the flippers. Simulation results obtained under three typical flipper faults demonstrate the effectiveness of the proposed fault-tolerant control method. This fault-tolerant control method ensures the safety of gliding robotic dolphins under complex deep-sea conditions.

A comparative study of three modes for realizing transmedia standing-and-hovering behavior in robotic dolphins

Three different hovering modes, namely, the caudal fin, pectoral fins, and multi fins, were utilized to achieve the standing-and-hovering behavior in robotic dolphins. A three-dimensional dolphin model, consisting of body, caudal fin, and symmetric pectoral fins, was used as the virtual swimmer to implement three hovering modes. A novel paddling motion was proposed, and a symmetric shape was designed of the pectoral fins. The hovering mechanisms of different modes were revealed, and the mapping relationships between different motion and performance parameters such as hovering height, efficiency, stability, and rapidity were established. The respective advantages of the three hovering modes were compared. The results showed that the caudal fin mode had the best hovering stability, while the pectoral fins mode had the best hovering rapidity. Moreover, it is worth noting that the multi fins mode had both the good hovering stability and rapidity. Therefore, the optimal hovering mode and motion parameters can be selected based on different expected objectives to achieve the best results. This study provides a new approach to break through the spatial barriers to movement of underwater robots and provides a solid hydrodynamic theoretical basis for the development of cross-medium robots with multiple hovering modes.

Calculation of Propulsive Motion for Two‐Jointed Bionic Robotic Dolphin

The cruising propulsion process of the bionic robotic fish under the swinging tail motion presents a strong periodic dynamic response, and accurate prediction of its performance is the key to the overall design. Taking the two‐jointed bionic robotic dolphin as the research object, five kinds of movement modes were designed, and the coupled analysis model of the propulsion motion of the bionic robotic dolphin was established based on the hydrodynamic and Lagrangian dynamics methods, and the hydrodynamic performance of different movement modes and its linear propulsion dynamic response process were investigated. The results show that the coupled analysis method proposed in the paper can accurately obtain the motion response parameters of the robotic dolphin as well as the forces and moments of each joint, and the speed error with the hydrodynamic simulation is controlled within 5%. The research method and results have good application value to guide the selection design and performance prediction of bionic robotic fish.

Robust Depth and Heading Control System for a Novel Robotic Dolphin With Multiple Control Surfaces

Robust Depth and Heading Control System for a Novel Robotic Dolphin With Multiple Control Surfaces

Performance Optimization for Bionic Robotic Dolphin with Active Variable Stiffness Control.

Aquatic animals such as fish and cetaceans can actively modulate their body stiffness with muscle to achieve excellent swimming performance under different situations. However, it is still challenging for a robotic swimmer with bionic propulsion mode to dynamically adjust its body stiffness to improve the swimming speed due to the difficulties in designing an effective stiffness adjustment structure. In this paper, based on the special torque mode of a motor, we propose an active variable stiffness control method for a robotic dolphin to pursue better swimming speed. Different from a variable stiffness structure design, a torque control strategy for the caudal motor is employed to imitate the physical property of a torsion spring to act as the variable stiffness component. In addition, we also establish a dynamic model with the Lagrangian method to explore the variable stiffness mechanism. Extensive experiments have validated the dynamic model, and then the relationships between frequency and stiffness on swimming performance are presented. More importantly, through integrating the dynamic model and torque actuation mode-based variable stiffness mechanism, the online performance optimization scheme can be easily realized, providing valuable guidance in coordinating system parameters. Finally, experiments have demonstrated the stiffness adjustment capability of the caudal joint, validating the effectiveness of the proposed control method. The results also reveal that stiffness plays an essential role in swimming motion, and the active stiffness adjustment can significantly contribute to performance improvement in both speed and efficiency. Namely, with the adjustment of stiffness, the maximum speed of our robotic dolphin achieves up to 1.12 body length per second (BL/s) at 2.88 Hz increasing by 0.44 BL/s. Additionally, the efficiency is also improved by 37%. The conducted works will offer some new insights into the stiffness adjustment of robotic swimmers for better swimming performance.

Flexible Bioelectronic Tag with a Kirigami‐Based Design for Crosstalk Suppression in Multimodal Sensing

AbstractOcean research currently relies heavily on bulky bioelectronic tags and sensory telemetry networks for data collection. Therefore, in this study, a compact and flexible waterproof bioelectronic tag with a kirigami (paper cutting)‐based design for underwater conductivity, temperature, depth, and strain sensing is designed and evaluated. Unlike invasive bioelectronic tags, the kirigami bioelectronic tag can be attached to robotic fish or aquatic animals without harming the host. The kirigami‐based design facilitates excellent stretchability and reduces stress within the sensor, thus inhibiting crosstalk induced by movement during multimodal sensing. A working bioelectronic tag is fabricated and tested. Notably, the performance of the kirigami sensors shows very little degradation even after >1000 stretching cycles. Specifically, the multimodal bioelectronic tag demonstrates a wide working pressure range of 0–5.0 MPa, and the kirigami design effectively suppresses signal coupling. The kirigami‐based bioelectronic tag is applied to a robotic dolphin and underwater environmental parameters and detailed movement parameters, such as swing angle, swing frequency, and typical gestures are detected simultaneously with high sensitivity and accuracy. Therefore, the device can be applied to a broad range of applications in various fields such as behavioral biology, ocean informatics, and underwater robotics.

A Torque Control Strategy for a Robotic Dolphin Platform Based on Angle of Attack Feedback.

Biological fish can always sense the state of water flow and regulate the angle of attack in time, so as to maintain the highest movement efficiency during periodic flapping. The biological adjustment of the caudal fin's angle of attack (AoA) depends on the contraction/relaxation of the tail muscles, accompanying the variation in tail stiffness. During an interaction with external fluid, it helps to maintain the optimal angle of attack during movement, to improve the propulsion performance. Inspired by this, this paper proposes a tail joint motion control scheme based on AoA feedback for the high-speed swimming of bionic dolphins. Firstly, the kinematic characteristics of the designed robot dolphin are analyzed, and the hardware basis is clarified. Second, aiming at the deficiency of the tail motor, which cannot effectively cooperate with the waist joint motor during high-frequency movement, a compensation model for the friction force and latex skin-restoring force is designed, and a joint angle control algorithm based on fuzzy inference is proposed to realize the tracking of the desired joint angle for the tail joint in torque mode. In addition, a tail joint closed-loop control scheme based on angle of attack feedback is proposed to improve the motion performance. Finally, experiments verify the effectiveness of the proposed motion control scheme.

Design and Analysis of a Bionic Gliding Robotic Dolphin

In this paper, we focus on the design and analysis of a bionic gliding robotic dolphin. Inspired by natural dolphins, a novel bionic gliding robotic dolphin is developed. Different from the existing ones, the gliding robotic dolphin developed in this work is specially introduced with a yaw joint to connect its three oscillating joints to improve maneuverability in both dolphin-like swimming and gliding motion. Consequently, the gliding robotic dolphin can realize several flexible motion patterns under the coordination of its flippers, yaw joint, oscillating joints, and buoyancy-driven modular. Thereafter, relying on the Newton-Euler method, a hybrid-driven dynamic model is constructed to further analyze the propulsive performance in both dolphin-like swimming and gliding motions. Finally, various simulations and experiments, including forward swimming, gliding, and turning in both dolphin-like swimming and gliding modes, are carried out to validate the effectiveness of the developed gliding robotic dolphin.

Quantifying the Leaping Motion Using a Self-Propelled Bionic Robotic Dolphin Platform

Kinematic analysis of leaping motions can provide meaningful insights into unraveling the efficient and agile propulsive mechanisms in dolphin swimming. However, undisturbed kinematic examination of live dolphins has been very scarce due to the restriction of close-up biological observation with a motion capture system. The main objective of this study is to quantify the leaping motion of a self-propelled bionic robotic dolphin using a combined numerical and experimental method. More specifically, a dynamic model was established for the hydrodynamic analysis of a changeable submerged portion, and experimental data were then employed to identify hydrodynamic parameters and validate the effectiveness. The effects of wave-making resistance were explored, indicating that there is a varying nonlinear relationship between power and speed at different depths. In addition, the wave-making resistance can be reduced significantly when swimming at a certain depth, which leads to a higher speed and less consumed power. Quantitative estimation of leaping motion is carried out, and the results suggest that with increase of the exiting velocity and angle, the maximum height of the center of mass (CM) increases as well; furthermore, a small exiting angle usually requires a much larger exiting velocity to achieve a complete exiting motion. These findings provide implications for optimizing motion performance, which is an integral part of underwater operations in complex aquatic environments.

Research on the Turning Maneuverability of a Bionic Robotic Dolphin

This paper studies four patterns for the maneuverability of robotic dolphins: turning with flapping flippers, turning with swing flippers, turning with head offset, and turning with head-flipper coordination. Turning maneuverability is one of the important evaluation indexes for the performance of underwater bionic robots, and existing literature has rarely theoretically or experimentally evaluated turning maneuverability for the latter two turning patterns. In this paper, we establish a dynamic model for the high maneuverability of underwater bionic robots and discuss the influence of motion design parameters, including the frequency of the pectoral fins and the offset angle of the head, on the turning maneuverability, focusing on the turning angular velocity and turning radius. To verify the effectiveness and control accuracy of the dynamic model, we develop a multidegree-of-freedom (multi-DOF) and high-maneuverability bionic robotic dolphin and test its maneuverability through experiments. Extensive experimental results demonstrate that the established dynamic model can successfully predict the turning maneuverability of robotic dolphins. In addition, the turning methods in this paper have better turning performance than some robotic fish. This paper provides a reference for the establishment of a maneuvering dynamics model for underwater bionic robots and a theoretical basis for the design of a turning maneuver control system.

The Research of Maneuverability Modeling and Environmental Monitoring Based on a Robotic Dolphin.

In this study, the C-turning, pitching, and flapping propulsion of a robotic dolphin during locomotion were explored. Considering the swimming action required of a three-dimensional (3D) robotic dolphin in the ocean, we propose a maneuverability model that can be applied to the flapping motion to provide precise and stable movements and function as the driving role in locomotion. Additionally, an added tail joint allows for the turning movement with efficient parameters obtained by a fluid-structure coupling method. To obtain a mathematical model, several disturbance signals were considered, including systematic uncertainties of the parameters, the perpetually changing environment, the interference from obstacles with effective fuzzy rules, and a sliding mode of control. Furthermore, a combined strategy of environment recognition was used for the positional control of the robotic dolphin, incorporating sonar, path planning with an artificial potential field, and trajectory tracking. The simulation results show satisfactory performance of the 3D robotic dolphin with respect to flexible movement and trajectory tracking under the observed interference factors.

Design and analysis of a novel tendon-driven continuum robotic dolphin

In this paper, a novel continuum robotic dolphin termed ‘ConRoDolI’ is proposed and developed. The biomimetic robot features dual tendon driving continuum mechanisms that are utilized to replicate the twisting and bending motions of the dolphin’s caudal vertebrae and thoracic vertebrae. More importantly, a central pattern generator based kinematics is analyzed to yield stable dolphin-like swimming. In the meantime, the relationship between the backbone shape and both the tendon length as well as position and orientation are explored. Furthermore, multimodal swimming gaits are designed to pave the way for a three-dimensional (3D) swimming decoupling solution, involving forwarding swimming, multiple yaw patterns, and multiple pitch patterns. All of these endow the robotic dolphin with 3D maneuverability. Finally, extensive experiments demonstrate the feasibility of the proposed biomimetic mechatronic design and control approach. The forward swimming speed is 0.44 body lengths per second (BL/s). The steering radius of the robot is about 0.11 BL with an angular velocity of 10°/s and the diving speed is about 0.13 BL/s. The average propulsion efficiency is about 0.6 with the maximum is over 0.8. The obtained results shed light on the improvement of aquatic maneuverability associated with new-concept underwater vehicles.

Cooperative Target Tracking in Aquatic Environment Using Dual Robotic Dolphins

This article proposes a modified rapidly exploring random tree (RRT)-based path planner and behavior-based cooperative tracking strategy for a dual robotic dolphin system to fulfill a cooperative target-tracking task. Specifically, with full consideration of both task requirements and mechatronic configuration, a robotic dolphin with a waist-caudal propulsive mechanism for thrust forces and differential bilateral flippers for maneuverability is developed. To satisfy the demand of fast path planning, a variant RRT algorithm is employed to generate feasible paths for the dual robotic dolphins with fewer waypoints, faster convergence speed, and better stability. Furthermore, a behavior-based approach in conjunction with centralized architecture is implemented to achieve high-level decision-making. Finally, simulations, analysis, as well as field experiments are carried out to verify the effectiveness of the proposed control scheme. The success of the experiments further offers insight into the mechanisms of cooperative multirobot target tracking in aquatic environments.

3-D Path Planning With Multiple Motions for a Gliding Robotic Dolphin

This paper presents a three-dimensional (3-D) path planning method that combines the gliding with dolphin-like motions for the gliding robotic dolphin. A specific task that the robot uses the gliding motion for long-distance cruise and the dolphin-like motion for maneuverable obstacle avoidance is employed. The results of simulations and aquatic experiments validate the full-state dynamic model and the specific task, further offer some theoretical supports for 3-D path planning. Further, the 3-D path planning method is composed of three main components: 1) gliding path generation; 2) improved Astar (A*) algorithm; and 3) segmented Bezier curve smoothing. First, the gliding path is generated autonomously with the kinematic constraints that are obtained via the simulations of dynamic model. Furthermore, when the obstacles are detected by the sonar, an improved A* algorithm is employed to avoid the obstacles. Afterward, considering the path planned by A* is unsmoothed, a segmented Bezier curve method is presented. Simulation results demonstrate the effectiveness of the method, offering valuable insight into the utilization of hybrid underwater robots in the context of real-time task execution.

Real-Time Path Planning and Following of a Gliding Robotic Dolphin Within a Hierarchical Framework

This paper proposes a novel hierarchical framework to achieve real-time path planning and following for a gliding robotic dolphin, including a learning-based path planner and an adaptive following controller. Subsequent to considering higher intelligence in unknown ocean environment, we present a novel hierarchical deep Q-network method to separately plan the collision avoidance path and the approach path, and also design different continuous-states under the kinematic constraints. Next, we adopt an improved line-of-sight method to obtain the desired points from planned path. More importantly, we derive a nonlinear control law based on backstepping technique, and specially avoid singularities in the law derivation using barrier Lyapunov function. In particular, the unknown model parameters are adaptively calculated to make the controller more robust. Finally, extensive simulation and experimental results verify the effectiveness of the proposed methods, providing a new idea to further ocean exploration.

Line-of-sight based three-dimensional path following control for an underactuated robotic dolphin

Line-of-sight based three-dimensional path following control for an underactuated robotic dolphin

Controlling the depth of a gliding robotic dolphin using dual motion control modes

This paper investigates the performance of the dual mode, namely flipper mode and central pattern generator (CPG) mode, for controlling the depth of a gliding robotic dolphin. Subsequent to considering the errors in dynamic models, we propose a depth control system that combines the line-of-sight (LOS) method with an adaptive control approach (ACA) to deal with uncertainties in the model parameters. First, we establish a full-state dynamic model to conduct simulations and optimize the parameters used in later aquatic experiments. Then, we use the LOS method to transform the control target from the depth to the pitch angle and employ the ACA to calculate the control signal. In particular, we optimize the ACA’s control parameters using simulations based on our dynamic model. Finally, our simulated and experimental results demonstrate not only that we can successfully control the robotic dolphin’s depth, but also that its performance was better than that of the CPG-based control, thus indicating that we can achieve three-dimensional motion by combining flipper-based and CPG-based control. The results of this study suggest valuable ideas for practical applications of gliding robotic dolphins.

Design and Manufacturing of Robotic Dolphin with Variable Stiffness Mechanism

Design and Manufacturing of Robotic Dolphin with Variable Stiffness Mechanism