Research On Motion Control Method Of Robotic Fish Propelled By Three-Degree-of-Freedom Pectoral Fins

Bionic robotic fish is an important platform for underwater observation and survey.It has the characteristics of high propulsion efficiency,strong maneuverability,and small impact on the environment compared with traditional underwater robots.So it has been extensively studied by researchers.Motion control is one of the basic problems in robotic fish research,which has an important impact on its ability to complete tasks.This thesis takes Carangiform robotic fish with the two pectoral fins developed by our laboratory as the object to study the motion control method of the robotic fish pectoral fins coordinated with 3 degrees of freedom.The main content has the following aspects:(1)The motion controller network of the robotic fish is established by the Central Pattern Generator(CPG),and the parameter conditions are determined which can produce various basic behaviors.There are three layers in the control network,the input conversion layer switches the mode,the middle layer mainly performs the operation of CPG,and the output conversion layer converts the control signal into a suitable steering gear signal.The middle layer constructs a CPG oscillation unit by using a set of linear state equations and sine output equations,and then constructs the CPG network through phase difference coupling.A hydrodynamic model based on the resistance mode and the lift mode under the coordinated pectoral fins propulsion is established by analyzing and modeling the different motion behaviors of the robotic fish.The simulation results show that the robot fish can swim stably in resistance mode or lift mode under the oscillator network.(2)A fixed depth controller based on lift mode is designed under the established CPG control network,which meets the control requirement that the error between actual depth and expected depth of robot fish is less than 10 cm.Firstly,the depth control is transformed into the question of controlling the flap angle and flap amplitude of pectoral fins.Then,a multi-input single-output(MISO)system is transformed into a compact form dynamic linearization model,and the pseudo gradient value is calculated by using the parameter estimation criterion function.Finally,a model-free adaptive control algorithm(MFAC)is designed by adding a parameter reset algorithm.The depth control of the robotic fish is realized by the gait generation,which controlled by the CPG parameters that are adjusted by the output value of algorithm.The simulation results show that under the model-free adaptive control scheme,the robotic fish can reach and maintain at the specified depth.