Robot fish with two-DOF pectoral fins and a wire-driven caudal fin

This paper presents a robot fish with a wire-driven caudal fin and a pair of pectoral fins. First, the design of the robot fish is presented. The caudal fin is driven through wire-driven mechanism. The pectoral fins can perform two degrees-of-freedom motions, i.e. flapping (roll) and feathering (pitch). The pectoral fins can move in labriform mode for propulsion, or for other purposes such as turning and diving. Second, the propulsion analysis models for caudal fin propulsion and pectoral fins propulsion are derived. Finally, three types of experiments are conducted. Experiment results show that the swimming speed of caudal fin propulsion and pectoral fin propulsion match the model predictions. Moreover, with the caudal fin propulsion alone, the robot fish can swim up to 0.66 BL/s (body length/second); with the pectoral fin propulsion alone, the robot fish can swim up to 0.26 BL/s. The pectoral fins can significantly improve the maneuverability of the robot fish. Without using the pectoral fins, the turning radius of the robot fish is 0.6 BL; with the pectoral fins, the turning radius is reduced to 0.25 BL.     

胸鳍推进机器鱼俯仰稳定性分析

胸鳍推进机器鱼的胸鳍在通过扑动产生推力的同时,也会产生纵向扰动,引起机身的俯仰运动,对应用产生一系列的影响.本文在传统潜艇稳定性概念的基础上建立了胸鳍推进机器鱼的俯仰稳定性模型,证明了机器鱼的俯仰运动系统是一个二阶线性系统;分析了由胸鳍扑动引入的扰动,证明其中包含常量分量、扑动频率的一倍频分量和二倍频分量.最后进行了样机的游动实验,实验结果间接证明了俯仰运动模型和胸鳍扑动扰动模型的正确性.     

Development of a biomimetic robotic fish and its control algorithm

This paper is concerned with the design of a robotic fish and its motion control algorithms. A radio-controlled, four-link biomimetic robotic fish is developed using a flexible posterior body and an oscillating foil as a propeller. The swimming speed of the robotic fish is adjusted by modulating joint's oscillating frequency, and its orientation is tuned by different joint's deflections. Since the motion control of a robotic fish involves both hydrodynamics of the fluid environment and dynamics of the robot, it is very difficult to establish a precise mathematical model employing purely analytical methods. Therefore, the fish's motion control task is decomposed into two control systems. The online speed control implements a hybrid control strategy and a proportional-integral-derivative (PID) control algorithm. The orientation control system is based on a fuzzy logic controller. In our experiments, a point-to-point (PTP) control algorithm is implemented and an overhead vision system is adopted to provide real-time visual feedback. The experimental results confirm the effectiveness of the proposed algorithms.     

A waypoint-tracking controller for a bionic autonomous underwater vehicle with two pectoral fins

This study aims to develop a waypoint-tracking control system for a biomimetic underwater vehicle (BUV). The BUV is propelled by wide paired pectoral foils, and each pectoral foil is driven by three independent fin rays. To simplify the control strategy, the maximum flapping amplitude of the pectoral fin is used to control the forward velocity, and a turning factor is defined for the manoeuvre control. Several swimming experiments are carried out to investigate the influence of the control parameters on the swimming performance of the prototype. Based on the results of the swimming experiments, a waypoint-tracking control system is proposed, which contains two layers: the velocity control layer and the heading angle control layer. A subdivision control method is adopted by the velocity control layer to get the maximum flapping amplitude. The fuzzy control method is employed by the heading angle control layer to obtain the turning factor for steering motion. Several waypoint-tracking experiments are carried out to verify effectiveness of the control system. The results show that the prototype can automatically reach the target area with the designed control system, even though the waypoints are arranged or randomly given.     

Maneuverability modeling and trajectory tracking for fish robot

This study develops a 6-DOF mathematical model for a robotic fish that considers surge, sway, heave, roll, pitch, and yaw. The model considers the conditions of a fish swimming in ocean current perturbations similar to the ocean current perturbations of the slender-body autonomous underwater vehicles. For swimming and turning behaviors, a nonlinear, dynamic, carangiform locomotion model is derived by using a planar four-link model. A 2-DOF barycenter mechanism is proposed to provide body stabilization and to serve as an actuating device for active control design. A barycenter control scheme is developed to change the center of gravity of the robot fish body by moving balancing masses along two axes. The projected torque on x and y axes propel pitch and roll angles to the desired settings. A Stabilizing controller, fish-tail mechanism, rigid body dynamics, and kinematics are incorporated to enable the fish robot to move in three dimensional space. Simulation results have demonstrated maneuverability and control system performance of the developed controller which is proposed to conduct path tracking of the robot fish as it swims under current perturbations.     

Controlling swimming and crawling in a fish robot using a central pattern generator

Online trajectory generation for robots with multiple degrees of freedom is still a difficult and unsolved problem, in particular for non-steady state locomotion, that is, when the robot has to move in a complex environment with continuous variations of the speed, direction, and type of locomotor behavior. In this article we address the problem of controlling the non-steady state swimming and crawling of a novel fish robot. For this, we have designed a control architecture based on a central pattern generator (CPG) implemented as a system of coupled nonlinear oscillators. The CPG, like its biological counterpart, can produce coordinated patterns of rhythmic activity while being modulated by simple control parameters. To test our controller, we designed BoxyBot, a simple fish robot with three actuated fins capable of swimming in water and crawling on firm ground. Using the CPG model, the robot is capable of performing and switching between a variety of different locomotor behaviors such as swimming forwards, swimming backwards, turning, rolling, moving upwards/downwards, and crawling. These behaviors are triggered and modulated by sensory input provided by light, water, and touch sensors. Results are presented demonstrating the agility of the robot and interesting properties of a CPG-based control approach such as stability of the rhythmic patterns due to limit cycle behavior, and the production of smooth trajectories despite abrupt changes of control parameters. The robot is currently used in a temporary 20-month long exhibition at the EPFL. We present the hardware setup that was designed for the exhibition, and the type of interactions with the control system that allow visitors to influence the behavior of the robot. The exhibition is useful to test the robustness of the robot for long term use, and to demonstrate the suitability of the CPG-based approach for interactive control with a human in the loop. This article is an extended version of an article presented at BioRob2006 the first IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics.     

Undulatory locomotion and effective propulsion for fish-inspired robot

Swimming, turning, and whip-sweeping propulsion for carangiform locomotion of a fish robot are investigated by means of a 4-link planar tail and an autonomous underwater vehicle (AUV)-like model. It is observed that excellent acceleration occurs when a whip sweeping behavior has been applied to the fish tail. The forward speed can even increases twice to the nominal swimming via the simulation study. The efficient movement is thus incorporated to the fish robot for agile movement. The robot's swimming patterns realize the effect in terms of the forward swimming, turning swimming, acceleration increasing, descended swimming, ascended swimming, depth regulating, and self-stabilization. Verification is accomplished by incorporating the 4-link planar tail, AUV-like model, and a two degree-of-freedom (DOF) barycenter mechanism. The four-link planar tail and 2-DOF barycenter mechanism act, respectively, as the thrust generator and stabilizing actuator for the fish robot. Sliding mode control (SMC) has been applied for three-dimensional (3D) trajectory tracking. Simulation results illustrate satisfactory performances of the fish robot in terms of the fish-like behaviors and maneuverability, which are due to the consequence of the mimicked predator-fish behaviors and performance robustness of the SMC for trajectory tracking under ocean current perturbations and modeling uncertainties.     

Design of a Bio-Inspired Autonomous Underwater Robot

The following paper presents the design and fabrication of an ostraciiform swimming robot and its navigation control and guidance system. Compared to other biomimetic vehicles, the chosen architecture has a lower propulsive efficiency but is easier to waterproof and capable to withstand greater pressures. To generate the alternating motion of the robot bio-inspired thruster, namely a plane fin, a transmission system was designed to replace the direct drive widely adopted in underwater biomimetic vehicles. The mechanical efficiency of two alternative mechanisms capable to actuate the fin were computed according to a preliminary sizing of the robot and its targeted swimming performances. Therefore, the more suitable solution was manufactured and installed aboard. At the same time, a proper navigation, guidance and control architecture (NGC) was designed and then integrated in the robot main controller. The proposed solution allows the vehicle to perform different missions autonomously once their profiles are received from the base station. Preliminary tests results and future works are discussed in the final conclusions.     

仿生机器鱼俯仰与深度控制方法

提出一种基于重心改变法的仿生机器鱼俯仰姿态与深度控制方法, 用于实现机器鱼水中的浮潜运动. 该方法利用一种可调整位置的配重块结构, 改变机器鱼的重心位置, 进而实现机器鱼俯仰姿态的调节. 在对机器鱼内部配重块位置和机器鱼俯仰角的关系进行分析的基础上, 对一定速度下机器鱼的深度与俯仰角的关系进行建模, 提出由于尾部形变引起的俯仰姿态变化的补偿方法. 文中给出机器鱼原形样机的相关实验, 分析验证配重块位置变化和机器鱼重心及其姿态的调整, 深度控制等在多种情况下的结果.     

一种水上行走机器人的设计与实现

研究了水上行走机器人的设计问题,提出了机器人驱动腿设计算法,给出了机器人结构、控制系统和 软件的设计方法和实例．设计并实现了一种采用双电机驱动、能转向和调速、通过红外信号遥控的水上机器人,并 对机器人进行了性能测试．该机器人仿生水黾重量轻、体积小、功耗低．实验表明其性能超过了现有同类机器人．     

无缆微型游动机器人驱动磁场系统的研究

提出了一种基于组合线圈结构的磁场系统驱动实验方案,以实现基于磁致伸缩薄膜驱动器的泳动微型机器人的磁控驱动与游动实验参数的检测．首先介绍了该组合线圈的功率优化与设计方法,然后分析了保证一定区域内磁场均匀性的技术方案,最后用ANSYS软件对所设计的组合线圈进行了仿真和验证．实验结果表明该组合结构磁场系统的性能可以满足无缆微型机器人的磁控驱动的设计要求．     

DCOB: Action space for reinforcement learning of high DoF robots

Reinforcement learning (RL) for robot control is an important technology for future robots since it enables us to design a robot’s behavior using the reward function. However, RL for high degree-of-freedom robot control is still an open issue. This paper proposes a discrete action space DCOB which is generated from the basis functions (BFs) given to approximate a value function. The remarkable feature is that, by reducing the number of BFs to enable the robot to learn quickly the value function, the size of DCOB is also reduced, which improves the learning speed. In addition, a method WF-DCOB is proposed to enhance the performance, where wire-fitting is utilized to search for continuous actions around each discrete action of DCOB. We apply the proposed methods to motion learning tasks of a simulated humanoid robot and a real spider robot. The experimental results demonstrate outstanding performance.     

Three-dimensional swimming tadpole mini-robot using three-axis Helmholtz coils

Electromagnetic-actuated robotic systems have been studied recently for special purposes. Because these systems use external magnetic fields to control their robots, the robots can have simple structures and move with much freedom. In particular, these electromagnetic actuation (EMA) systems are being widely adopted for the actuation of biomedical mini-robots and microrobots for minimally invasive surgery (MIS) and diagnosis. We previously reported, as a feasible biomedical robot, the biomimetic swimming tadpole mini-robot, which can only swim above water. Indeed, the two-dimensional (D) plane swimming tadpole mini-robot is limited in its use because of its motility in the 2D plane. Therefore, this paper proposes a 3D swimming tadpole mini-robot that can move freely in water. First, in the proposed 3D swimming tadpole mini-robot, the buoyancy force was regulated for subaqueous swimming, and the permanent magnet was rearranged for precise movement. Second, to attain a 3D swimming motion, the actuation mechanism of the robot was developed using an EMA system. Finally, various experiments verified that the proposed 3D swimming tadpole mini-robot can swim freely in a 3D water environment.     

基于功能／行为集成的自主式移动机器人进化控制体系结构

本文针对自主式移动机器人控制体系结构中两类典型方法的不足,提出了一种进化控制体系 结构,实现了基于AI模型的方法与基于行为的方法的优势互补．文中阐述了进化控制的思想 ,并应用于移动机器人控制结构的设计．该结构使移动机器人具备良好的学习和适应能力、 较快的响应速度,同时拥有较好的理性和完成给定任务的能力．     

6-DOF并联机器人控制算法结构化分析与设计

为了实现对六自由度并联机器人位置速度算法的控制,针时控制算法采用了软件工程的原理和方法进行了分析,并对机器人运动特性进行了研究.根据运动特性对位置与速度的控制算法进行了解析,提出位置反解的控制策略,给出了功能分析的DFD模型和软件结构化设计模型SC图.描述了算法的详细设计及实现,采用结构化语言表达工具,并对实现中重要的部分细节进行了细致的研究,其结果达到了位置速度控制的目的及机器人控制算法的软件结构化设计.     

Amphibious Pattern Design of a Robotic Fish with Wheel‐propeller‐fin Mechanisms

This paper is devoted to the underwater and terrestrial locomotion aspects of an amphibious robotic fish propelled by modular fish‐like propelling units and a pair of hybrid wheel‐propeller‐fin mechanisms. According to the mechanical structure and locomotion characteristics of the robot, a central pattern generator (CPG) network comprising coupled oscillators is employed to produce signals for swimming, crawling, as well as transitions between them. Specifically, a set of four key parameters including a tonic input drive, a direction factor, and two pitch factors is introduced to serve as input to the CPG network. Meanwhile, a finite state machine is built to trigger locomotor pattern transitions. Field tests on the amphibious patterns and autonomous water‐land transition demonstrate the effectiveness of the adopted CPG‐based control architecture. The latest results show that the robot attained a maximum advancing speed of 1.16 m/s (corresponding to 1.66 body lengths per second), a minimal turning radius of approximately 0.55 m (corresponding to 0.79 body lengths) on land, as well as an average rolling speed of 204 degrees per second in an alligator‐like roll maneuver. It is also found that the dolphin‐like dorsoventral swimming could provide an increase of 10.3% in speed compared to the fish‐like carangiform swimming on the same propulsion platform.     

Design and performance evaluation of a biomimetic microrobot for the father–son underwater intervention robotic system

Underwater intervention is a favorite and difficult task for AUVs. To realize the underwater manipulation for the small size spherical underwater robot SUR-II, a father–son underwater intervention robotic system (FUIRS) is proposed in our group. The FUIRS employs a novel biomimetic microrobot to realize an underwater manipulation task. This paper describes the biomimetic microrobot which is inspired by an octopus. The son robot can realize basic underwater motion, i.e. grasping motion, object detection and swimming motion. To enhance the payload, a novel buoyancy force adjustment method was proposed which can provides 11.8 mN additional buoyancy force to overcome the weight of the object in water. Finally, three underwater manipulation experiments are carried out to verify the performance of the son robot. One is carried by swimming motion and buoyancy adjustment; the other two are only carried by buoyancy adjustment. And the experimental results show that the son robot can realize the underwater manipulation of different shape and size objects successfully. The swimming motion can reduce the time cost of underwater manipulation remarkably.     

AmphiBot I: an amphibious snake-like robot

This article presents a project that aims at constructing a biologically inspired amphibious snake-like robot. The robot is designed to be capable of anguilliform swimming like sea-snakes and lampreys in water and lateral undulatory locomotion like a snake on ground. Both the structure and the controller of the robot are inspired by elongate vertebrates. In particular, the locomotion of the robot is controlled by a central pattern generator (a system of coupled oscillators) that produces travelling waves of oscillations as limit cycle behavior. We present the design considerations behind the robot and its controller. Experiments are carried out to identify the types of travelling waves that optimize speed during lateral undulatory locomotion on ground. In particular, the optimal frequency, amplitude and wavelength are thus identified when the robot is crawling on a particular surface.     

Robot Control Optimization Using Reinforcement Learning

Conventional robot control schemes are basically model-based methods. However, exact modeling of robot dynamics poses considerable problems and faces various uncertainties in task execution. This paper proposes a reinforcement learning control approach for overcoming such drawbacks. An artificial neural network (ANN) serves as the learning structure, and an applied stochastic real-valued (SRV) unit as the learning method. Initially, force tracking control of a two-link robot arm is simulated to verify the control design. The simulation results confirm that even without information related to the robot dynamic model and environment states, operation rules for simultaneous controlling force and velocity are achievable by repetitive exploration. Hitherto, however, an acceptable performance has demanded many learning iterations and the learning speed proved too slow for practical applications. The approach herein, therefore, improves the tracking performance by combining a conventional controller with a reinforcement learning strategy. Experimental results demonstrate improved trajectory tracking performance of a two-link direct-drive robot manipulator using the proposed method.