Amphibious Spherical Robot Research Articles

A Deep Reinforcement Learning-Based Decentralized Hierarchical Motion Control Strategy for Multiple Amphibious Spherical Robot Systems With Tilting Thrusters

A Deep Reinforcement Learning-Based Decentralized Hierarchical Motion Control Strategy for Multiple Amphibious Spherical Robot Systems With Tilting Thrusters

Design of an Amphibious Spherical Robot Driven by Twin Eccentric Pendulums With Flywheel-Based Inertial Stabilization

This article presents the design of an amphibious spherical robot with a sole focus on its mechanical design to achieve high torque, versatile motion modes, compact and lightweight structure, and high stability and traction, without relying on optimal control strategies. To achieve this, we unified the use of twin eccentric pendulums for high torque, flywheels for inertial stabilization and enhanced traction, and flywheel brakes for instantaneous torque to overcome obstacles. Dynamic analysis is performed, which gives an insight into the robot's motion and helps in making design decisions. High-level and low-level design decisions are discussed based on robot dynamics and intuition. Finally, a prototype of the designed spherical robot is assembled, and subjected to performance evaluation through terrestrial and aquatic locomotion experiments. The experimental results validated our design decisions, showing the design approach yields a spherical robot with stable and versatile locomotion, building the foundation for further improvements via optimal control and sensing.

Dynamic Analysis and Path Planning of a Turtle-Inspired Amphibious Spherical Robot.

A dynamic path-planning algorithm based on a general constrained optimization problem (GCOP) model and a sequential quadratic programming (SQP) method with sensor input is proposed in this paper. In an unknown underwater space, the turtle-inspired amphibious spherical robot (ASR) can realise the path-planning control movement and achieve collision avoidance. Due to the special underwater environments, thrusters and diamond parallel legs (DPLs) are installed in the lower hemisphere to realise accurate motion control. A propulsion model for a novel water-jet thruster based on experimental analysis and a modified Denavit-Hartenberg (MDH) algorithm are developed for multiple degrees of freedom (MDOF) to realize high-precision and high-speed motion control. Simulations and experiments verify that the effectiveness of the GCOP and SQP algorithms can realize reasonable path planning and make it possible to improve the flexibility of underwater movement with a small estimation error.

Design, Implementation and Control of an Amphibious Spherical Robot

Design, Implementation and Control of an Amphibious Spherical Robot

A Virtual Linkage-Based Dual Event-Triggered Formation Control Strategy for Multiple Amphibious Spherical Robots in Constrained Space With Limited Communication

Aiming to deal with the formation maintaining in constrained space for a group of robots, this paper proposed a virtual linkage-based dual event-triggered formation control strategy. Based on the idea of virtual linkage and event-trigger, a dual event trigger is proposed to guarantees robot formation keeping and collision avoidance. Unlike classical event-triggered control, the control strategy triggered by the detection of the state of virtual linkage determine the motion mode of the robot, which can reduce the control updating and eliminate continuous communication between robots. Moreover, an adaptive control law inspired by the motion of a simple pendulum was developed to adjust the given angle of the virtual linkage in the case that the multi-robot system pass the restricted region. Finally, to validate the performance of the formation control strategy, simulations and a series of experiments in an indoor swimming pool are presented. The results demonstrate the robustness and feasibility of the proposed formation control strategy.

An Improved Backstepping Controller with an LESO and TDs for Robust Underwater 3D Trajectory Tracking of a Turtle-Inspired Amphibious Spherical Robot

In this paper, a double closed-loop backstepping controller is designed for 3D trajectory tracking of a turtle-inspired amphibious spherical robot suffering from problems that include model uncertainties, environmental disturbances, and unmeasured velocity. The proposed controller scheme tackles three primary challenges: the differentiation explosion of the traditional backstepping method, unmeasured velocity, and the consideration of lumped disturbances. Beginning with an outer-loop backstepping controller, a virtual feedback variable is constructed to simplify the design of the backstepping controller. Meanwhile, to avoid the problem of differentiation explosion, tracking differentiators (TDs) are utilized to estimate the differentiation of the desired velocity in an inner-loop backstepping controller. Moreover, there are some uncertainty disturbances in the task of tracking the trajectory of a turtle-inspired amphibious spherical robot (TASR), such as the parameters of the hydrodynamic model and environmental disturbances. A linear extended state observer (LESO) is designed to estimate and compensate for the lumped disturbances. Furthermore, as the velocity states of the TASR are unmeasured, the LESO is also utilized to estimate the velocity states in surge, yaw, and heave degrees. Therefore, the TASR only needs to supply its position and orientation information for the trajectory tracking task. Note that this paper details both the design process of the proposed controller and a rigorous theoretical analysis. In addition, numerical simulations are conducted, and the results demonstrate the feasibility and superiority of the proposed method.

Design, modeling and control of a miniature bio-inspired amphibious spherical robot

It is a huge challenge for an amphibious robot with a high locomotory performance to locomote in amphibious environments, including crawling on rough terrains, maneuvering underwater, and launching and landing motion between land and water. To deal with such a challenge, a miniature bio-inspired Amphibious Spherical Robot (ASRobot) with a Legged, Multi-vectored Water-jet Composite Driving Mechanism (LMWCDM) has been designed. In this paper, locomotory performance of the robot in amphibious field environments is studied. First, a simplified kinematic model was built to study crawling gaits, and with an online adjustment mechanism, the gaits were adjusted, enabling the robot to climb up slopes more stably. Then, using a dynamic underwater model, a real-time dynamic thrust vectoring allocation strategy is proposed to generate the water-jet thrust and joint angles using desired forces and torques computed by four parallel PID algorithms. Finally, a set of experiments were carried out to evaluate the performance of on land locomotion and underwater locomotion. Further, outdoor locomotion experiments including crawling on various terrains, launching and landing motion, were conducted in field environments. The results demonstrate that the robot prototype possesses the high locomotory performance which endows its wide application of disaster rescue, reconnaissance and resource exploration in amphibious environments.

Design and Modelling of an Amphibious Spherical Robot Attached with Assistant Fins

Mobile robots that can survive in unstructured wildernesses is essential in many applications such as environment detecting and security surveillance. In many of these applications, it is highly desirable that the robot can adapt robustly to both terrestrial environment and aquatic environment, and translocate swiftly between various environments. A novel concept of amphibious spherical robot with fins is proposed in this paper, capable of both terrestrial locomotion and aquatic locomotion. Unlike the traditional amphibious robots, whose motions are commonly induced by propellers, legs or snake-like tandem joints, the proposed amphibious spherical robot utilizes the rolling motion of a spherical shell as the principal locomotion mode in the aquatic environment. Moreover, spinning motion of the spherical shell is used to steer the spherical robot efficiently and agilely; several fins are attached to the outer spherical shell as an assistance to the rolling motion. These two motion modes, rolling and spinning, can be used unchangeably in the terrestrial environment, leading to a compact and highly adaptive design of the robot. The work introduced in this paper brings in an innovative solution for the design of an amphibious robot.

Study on the Autonomous Multirobot Collaborative Control System Based on Spherical Amphibious Robots

The study on the multirobot collaborative control method has broad application prospect and value in the field of robotics. To adapt to a variety of working environments and higher efficiency, this article designed the autonomous multirobot collaborative control system based on spherical amphibious robots. First, this article proposed the formation strategy for spherical amphibious multirobot and used linear quadratic regulator algorithm to adjust the robot trajectory. Then, this article used XBee wireless communication with excellent communication performance under low noise ratio conditions to complete real-time information sharing of multirobot. Finally, based on the theoretical analysis and calculation, a series of land and underwater evaluation experiments were carried out to verify the feasibility of autonomous multirobot collaborative control system. The experimental results showed that the spherical amphibious multirobot could realize collaborative control accurately under different environments according to the predetermined trajectory.

A Fuzzy PID Algorithm for a Novel Miniature Spherical Robots with Three-dimensional Underwater Motion Control

We proposed and developed a small bionic amphibious spherical robot system for tasks such as coastal environment monitoring and offshore autonomous search and rescue. Our third-generation bionic small amphibious spherical robots have many disadvantages, such as the lack of maneuverability and a small operating range. It is difficult to accomplish underwater autonomous motion control with these robots. Therefore, we proposed a fourth-generation amphibious spherical robot. However, the amphibious spherical robot developed in this project has a small and compact design, with limited sensors and external sensing options. This means that the robot has weak external information collection capabilities. We need to make the real time operation of the robot’s underwater motion control system more reliable. In this paper, we mainly used a fuzzy Proportional-Integral-Derivative (PID) control algorithm to design an underwater motion control system for a novel robot. Moreover, we compared PID with fuzzy PID control methods by carrying out experiments on heading and turning bow motions to verify that the fuzzy PID is more robust and exhibits good dynamic performance. We also carried out experiments on the three-dimensional (3D) motion control to validate the design of the underwater motion control system.

Collaboration and Task Planning of Turtle-Inspired Multiple Amphibious Spherical Robots.

Amphibious Spherical Robots (ASRs) use an electric field to communicate and collaborate effectively in a turbid water of confined spaces where other mode communication modalities failed. This paper proposes an embedded architecture formation strategy for a group of turtle-inspired amphibious robots to maintain a long distance-parameterized path based on dynamic visual servoing. Inspired by this biological phenomenon, we design an artificial multi-robot cooperative mode and explore an electronic communication and collaborate devices, the control method is based in particular on underwater environment and also conduct a detailed analysis of control motion module. The objectives of control strategies are divided into four categories: The first strategy is that the leader robot controls the action of the overall robots to maintain collaborate together during motion along a desired geometric path and to follow a timing law that the communication efficiency and the arrival times to assigned sites. Furthermore, we design an adaptive visual servoing controller for trajectory tracking task, taking into account system dynamics with environment interactions. After that, the third strategy is a centralized optimization algorithm for the redistribution of target mission changes. Finally, this paper also proposes a new method of control strategies in order to guarantee that each robot in the team moves together according to the preset target toward its location in the group formation based on communication and stability modules.

Development and control of articulated amphibious spherical robot

In this paper, we proposed an amphibious spherical robot that can search and rescue from uneven terrain and also move in narrow underwater spaces. This paper presents three control methods for an articulated amphibious spherical robot. The first is a full-dimensional that is adapted the robot to the complex amphibious terrain, in this method, relying on a novel drive mode of mecanum wheels, the power required for the movement comes from the friction generated by mecanum wheels and the spherical shell. The second control method is modeling based on a unit quaternion motion control algorithm to realized 6 Degrees of Freedoms (DoFs) movement mode. The last control algorithm is according to Archimede Buoyancy Principle (ABP) and Fuzzy Control (FC) algorithm by controlling the air density of the spherical capsules in the lower hemispheres, the relationship between buoyancy and gravity is controlled to achieve the functions of floating and diving. Experiments are performed to demonstrate the effectiveness of the proposed methods and the developed robot.

Design, modeling and experimental evaluation of a legged, multi-vectored water-jet composite driving mechanism for an amphibious spherical robot

This paper designs a novel legged, multi-vectored water-jet composite driving mechanism (LMWCDM) for the amphibious spherical robot (ASRobot) and presents modeling and experimental evaluation of this composite driving mechanism. In order to crawl on land flexibly, the robot was designed in SolidWorks and simulated in ADAMS environment with the sit to stand motion and a crawling gait. Then the simulation results, such as driving torques, guided the selection of servomotors in different joints. In aquatic environment, the dynamic modeling of ASRobot was analyzed by synthesizing the propulsive vectors of four propellers in each workspace of legs. Simplistically, multiple underwater locomotion, such as longitudinal and lateral motion, rotary motion, sinking and floating motion and cruising motion, were proposed. Thus, using a six-axis force/torque sensor at the equivalent mass center, a force and torque measuring mechanism was developed to obtain the direct propulsive effect and validate the modeling of the driving system. To evaluate the robot design and selection of servomotors, experiments of the sit to stand motion and crawling motion were conducted. Underwater testing experiments of LMWCDM were carried out to verify the modeling of rotary motion, sinking and floating motion. Besides, underwater test of the robot prototype also proved the highly flexible and swift motion.

Performance evaluation of spherical robot for amphibious applications

Aiming at exploration tasks in complex amphibious environments, our previous researches proposed and developed an amphibious spherical robot, and the robot is capable of motion on land and swim in underwater. In this paper, focus on robotic applications on various terrains of amphibious robot, three quadruped gaits and an adaptive control method were designed, implemented and evaluated for our amphibious spherical robot. Firstly, a simplified locomotion model of the amphibious spherical robot was established, and three types of on-land locomotion gait were designed for the robot, then the adopted gait was adaptively adjusted with attitude compensation of robot. And simultaneously, an adaptive control algorithm was designed to control the amphibious spherical robot in underwater environment, which has good robustness and adaptability of disturbances in underwater environment. Finally, some amphibious evaluation experiments on robotic on-land and underwater motion performance indicated that the amphibious spherical robot was capable of moving stably on-land and in underwater environments, which enhanced its mobility and viability.

Robust RGB-D Camera and IMU Fusion-based Cooperative and Relative Close-range Localization for Multiple Turtle-inspired Amphibious Spherical Robots

In the narrow, submarine, unstructured environment, the present localization approaches, such as GPS measurement, dead-reckoning, acoustic positioning, artificial landmarks-based method, are hard to be used for multiple small-scale underwater robots. Therefore, this paper proposes a novel RGB-D camera and Inertial Measurement Unit (IMU) fusion-based cooperative and relative close-range localization approach for special environments, such as underwater caves. Owing to the rotation movement with zero-radius, the cooperative localization of Multiple Turtle-inspired Amphibious Spherical Robot (MTASRs) is realized. Firstly, we present an efficient Histogram of Oriented Gradient (HOG) and Color Names (CNs) fusion feature extracted from color images of TASRs. Then, by training Support Vector Machine (SVM) classifier with this fusion feature, an automatic recognition method of TASRs is developed. Secondly, RGB-D camera-based measurement model is obtained by the depth map. In order to realize the cooperative and relative close-range localization of MTASRs, the MTASRs model is established with RGB-D camera and IMU. Finally, the depth measurement in water is corrected and the efficiency of RGB-D camera for underwater application is validated. Then experiments of our proposed localization method with three robots were conducted and the results verified the feasibility of the proposed method for MTASRs.

Hydrodynamic Analysis-Based Modeling and Experimental Verification of a New Water-Jet Thruster for an Amphibious Spherical Robot.

Thrusters are the bottom actuators of the amphibious spherical robot, and play an important role in the motion control of these robots. To realize accurate motion control, a thrust model for a new water-jet thruster based on hydrodynamic analyses is proposed in this paper. First, the hydrodynamic characteristics of the new thruster were numerically analyzed using computational fluid dynamics (CFD) commercial software CFX. The moving reference frame (MRF) technique was utilized to simulate propeller rotation. In particular, the hydrodynamics of the thruster were studied not only in the axial flow but also in oblique flow. Then, the basic framework of the thrust model was built according to hydromechanics theory. Parameters in the basic framework were identified through the results of the hydrodynamic simulation. Finally, a series of relevant experiments were conducted to verify the accuracy of the thrust model. These proved that the thrust model-based simulation results agreed well with the experimental results. The maximum error between the experimental results and simulation results was only 7%, which indicates that the thrust model is precise enough to be utilized in the motion control of amphibious spherical robots.

DESIGN AND IMPLEMENTATION OF THE VISUAL DETECTION SYSTEM FOR AMPHIBIOUS ROBOTS

Aiming at application requirements of our spherical amphibiousrobot, which has one type of propulsion system to be used bothon land and in water, an improved tracking learning detection(TLD) algorithm is designed and implemented, so as to improve therobustness and environmental adaptability of its visual detectionsystem.

The communication and stability evaluation of amphibious spherical robots

This paper aims to improve the collaboration ability and stability of amphibious spherical robots (ASRs). According to our previous researches, robots have no communication or control stability module. This study designed a new torque gyro control stability and an artificial electronic communication module devoted to allowing the robot to both move on land and underwater, which used a gyro sensor to design a closed-loop control module to perform terrestrial locomotion efficiently. Regarding the spherical robot mechanical structure and dynamic model, the robot communication module is designed, and the physical robot is set up to complete specific experiments. In addition, it is necessary to analyze the underwater and land motion to evaluate the performance of the robot stability motion and communication module, which includes the gait stability and velocity, and predicts the effects of the key parameters, such as electrode distance and emitter current of the amphibious spherical robot when it moves in underwater or on land. We also characterize communicate performance of the robots in still water with obstacles and natural water conditions.

Underwater motion characteristics evaluation of multi amphibious spherical robots

Information exchanges and cooperative movements of multi robots have become a hot topic in robotics. To improve the performance and working efficiency of our amphibious spherical robot, the leader–follower method, which could realize the coordinated movement and formation keeping for three or more robots, was adopted in this paper. Firstly, this paper depicts the formation design of multi robots, and the formation system is made up of two or three robots which can formed longitudinal formation, linear formation and triangular formation. And then, the formation strategy of multi robots based on leader–follower method was depicted and analyzed, including the principle of relative attitude observation and the design of kinematic controller. Finally, based on the theoretical analysis and calculation, a series of underwater experiments were carried out to test the performance of amphibious spherical multi robots with different formations; these experiments included longitudinal formation motion test, linear formation motion test, and triangular formation motion test. The experimental results demonstrated that the multi robots could realize different underwater formation motion accurately.

Visual positioning system for small-scaled spherical robot in underwater environment

Aiming at application requirements of our small-scaled spherical amphibious robots, a visual positioning system adopting the model of depth image and feature fusion was designed and implemented in this paper. Considering the narrow load space, the limited structure space and the specialized underwater application scenarios of the spherical robot (the diameter of the upper and lower hemisphere is 320 and 350 mm, respectively), a Time of Flight RGB-D camera was used, and the color image and depth image could be acquired, thus the position of objective could be calculated from image information, a calibration experiment for distance correction was designed to improve the accuracy of the positioning system. Based on the theoretical analysis and calculation, a series of underwater experiments were carried out to test the performance of the proposed positioning method. Experimental results confirmed the feasibility of the proposed visual positioning method, and the maximum error between the actual positioning result and the reference value is less than 7 mm, which could meet future demands of our amphibious spherical robot in biological monitoring and multi robot cooperation.