Research On The Precise Control Method Of Plane Motion Trajectory Of Robotic Fish Propelled By Pectoral Fin And Caudal Fin

Biomimetic robotic fish is one of the important research directions for underwater robots,and has broad application prospects in fields such as underwater biological observation and military reconnaissance.Due to the complexity of the fluid environment in which the robotic fish operates,the control of the trajectory of the robotic fish has always been a key research issue in this field.This paper investigates the precise control algorithm for the planar motion of a biomimetic robotic fish propelled by a 3-degree of freedom pectoral fin,flexible body,and caudal fin.The main contents are as follows:(1)A new 3-degree of freedom pectoral fin propulsion mechanism was designed,and given the motion law of the robotic fish pectoral fin,a propulsion mode in which the lift generated in the z-axis direction during the robotic fish pectoral fin propulsion was close to zero was obtained.Firstly,by observing the movement of the pectoral fin of real fish,the design requirements of the pectoral fin driving mechanism and the movement rules of each joint of the pectoral fin driving mechanism are formulated,and then the propulsion force generated during the entire pectoral fin movement process is obtained through the calculus method.The propulsion force generated by the tail fin of a robotic fish during its motion under ideal conditions is calculated using the momentum theorem.According to the obtained method for calculating the propulsive force of the robotic fish pectoral fin,using computer simulation,by setting the expected value of the z-axis lift force of the robotic fish to zero,and adjusting the swing angle of the pectoral fin with the help of a PID controller,it is obtained that the swing angle of the pectoral fin should be 65 degrees when the robotic fish swims horizontally.(2)Under the condition that the robot fish is regarded as a spatial ellipsoid with uniform mass distribution,a hydrodynamic model of pectoral and caudal fin cooperative propulsion is established,and the mapping relationship between the motion parameters of the robot fish’s pectoral and caudal fins and the overall motion parameters of the robot fish is obtained.The cooperative motion law of the pectoral and caudal fins is further designed.The mass and inertial force matrices,Coriolis force and centripetal force matrices,fluid resistance matrices,restoring force matrices,and driving force matrices of the robotic fish were determined through theoretical calculations,thereby completing the construction of the dynamic model.Based on this,the relationship between the motion amplitude difference of the pectoral fins on both sides of the robotic fish and the turning angular velocity of the robotic fish was analyzed through simulation.Furthermore,the cooperative motion law of the pectoral and caudal fins of the robot fish in planar motion is formulated,reducing the control input parameters of the pectoral and caudal fins of the robot fish.(3)A composite tracking control algorithm for robot fish planar motion trajectory is designed,which combines proportional guidance control and linear active disturbance rejection controller(Linear Active Disturbance Rejection Control,LADRC).The proportional guidance part realizes the conversion of robot fish posture error to the desired swimming speed and yaw angular speed of the robot fish;The LADRC part controls the robotic fish to achieve closed-loop control of the swimming speed and yaw rate.By setting the desired trajectory of the robotic fish as a planar "8" shaped curve,a combination of simulation and physical experiments was used to verify the effectiveness of the designed control system.