Research On Posture Control Of Biomimetic Robotic Fish Based On PID Theory

In recent years,the biomimetic robotic fish plays a key role in underwater tasks,such as pipeline patrolling and water quality monitoring,which may make the precise motion control of the biomimetic robotic fish become one of the research hotspots in the field of underwater robot system.The biomimetic robotic fish relies on the interaction of fish body and fins with water to produce fluid dynamics.Due to the interference of water environment and the nonlinear dynamics of the biomimetic robotic fish,the accuracy of the posture(position and direction are collectively referred to posture)control of the biomimetic robotic fish is relatively low.In this paper,the posture control of the biomimetic robotic fish is studied by taking the three-joints Carangiform robotic fish as the research object.The main research contents are as follows:1.According to the structure of three-joints biomimetic robotic fish,the coordinate system is established,and the transformation matrices from the world coordinate system to the joint zero body coordinate system and the transformation matrices between each joint body coordinate system are solved.Then,in the process of robotic fish swimming,the joint kinematics analyses of angular velocity,velocity,angular acceleration and linear acceleration are carried out,and the dynamic model based on Kane equation is proposed.2.In view of the posture control of the biomimetic robotic fish,the angle error,the range error and error change rate,which are conducted by robotic fish expected posture and actual posture,are as inputs of outer loop PID controller.The angle error is formed by direction angle and line of sight angle.Outer loop PID controller outputs-the expected speed and angular velocity-are as the inner PID controller inputs.The orders of speed and angular velocity are as the outputs of the inner loop PID controller.The cascade PID algorithm is used to reduce the interference of water environment and to improve the control precision of robotic fish's posture.The corresponding strategies are written by Microsoft Visual Studio 2010,and they are applied to the simulation platform of URWPGSim2 D software and the platform of multi-underwater robots cooperative control system respectively.The results prove the rationality and effectiveness of the proposed algorithm.3.The fixed proportion,integral,differential coefficient of inner loop in cascade PID cannot be able to appropriately apply to the complicated water environment.To decrease the difficulty of setting control parameters,the posture control of robotic fish is improved self-adaptively.Fuzzy control adjusts the control parameters of inner loop of the cascade PID algorithm in real time.The angle error,the range error and error change rate are as fuzzy controller inputs,while proportional,integral,differential coefficients are as the outputs of fuzzy controller.The robotic fish posture control precision is improved at the same time the response time is shorten by utilizing the fuzzy self-adaptive cascade PID algorithm.