Hydrodynamics Analysis And Motion Control Of Robotic Fish With Two Degrees Of Freedom Pectoral-Fin

Recently,biomimetic robotic fish has become a topic issue in the field of robot since it can be used in many applications such as map building,ecological monitoring,military surveillance,rescue,etc..According to the propulsion method,biomimetic robotic fish can be classified into two types,named body/caudal fin mode(BCF)and median/paired fin mode(MPF).In the early works,the BCF mode was the focus of the research.Lately,MPF mode attracted more attention because it has advantage over BCF mode in maneuverability and stability of motion.Three categories of MPF robotic fish have been successfully developed such as multi-fin oscillating,pectoral-fin flapping or/and gliding,and long-fin undulating,respectively.This thesis considers the swimming mechanism of robotic fish propelled by pectoral fins with two degree of freedom.The main contents are as follows.A biomimetic robotic box-fish,in which each pectoral fin has two degree of freedom(DOF),had been designed,and then the kinematics models of them are proposed.Combined with the advantages of multi-fin oscillating and BCF,the proposed pectoral fin can sway from the front to the behind and roll around the axis of it,which preferably matches the true complex behaviors of box-fish.On this basis,the kinematics models are designed for each pectoral fin and the caudal fin,respectively.The hydrodynamics model had been established for the robotic box-fish and then its swimming mode had been analyzed.Under the dragging mode,the hydrodynamics models are established for the single pectoral fin,both side of pectoral fin,caudal fin and the cooperative propulsion of them,respectively.Again,the conditions are given for robotic box-fish to swim forward,turn with given radius,and turn on the spot and stop,respectively,by analyzing the results of numerical simulation.The results of experiments verified the validity of the proposed method.Based on the central pattern generator(CPG)method,another kinematics model of robotic box-fish had been established,which carries out the flexible switching among different swimming behaviors.By employing the advantages of CPG method in flexibility of mode switching and environment adaptability,the controller of robotic box-fish is designed based on CPG,in which five CPG units are contained.Through activating or prohibiting the relevant CPG units,the basic behaviors such as swimming forward,turning and stopping are achieved,respectively.As the motion parameters abruptly change or the environment disturbance randomly take place,the robotic box-fish can smoothly switch among the different basic behaviors.The results of experiments verified the validity.