Modeling And Control Of A Biomimetic Wire-driven Soft Robotic Fish

Recently,underwater robot technology has become a key factor in the development of national marine strategy.As a kind of underwater robot,the bionic robot fish is free from the disadvantages of traditional propeller driven underwater robots,such as high noise,low efficiency and tremendous energy consumption.Robotic fish is a new type of underwater robot with low noise,fast speed,high efficiency and flexibility.It can adapt to a variety of working conditions for long working time.The body of bionic robotic fish is generally rigid.The complexity of its mechanical transmission increases with the required degrees of freedom and the robustness of the robotic fish decreases as a result.In this paper,a new wire-driven soft robotic fish is proposed,which can better simulate the motion curve of real fish.Based on the design of this soft robotic fish,the modeling and controller design are carried out.Main research contents and contributions are summarized as follows.1.A new type of soft robotic fish design driven by a biomimetic propulsor is proposed,and corresponding kinematic model is built.The propulsor is composed of a soft tail made of silica gel and two controlling wires.By controlling the two wires,the soft tail can complete oscillatory motion.This robotic fish is simple in structure and easy to manipulate.The kinematic model is built based on Lighthill's elongated body theory.The simulation results show that the swing curve of the soft fish tail fits well with the actual swing curve of the fish body,and the cruising speed is faster than that of the multi-joint robotic fish,which verifies the effectiveness of the wire-driven design.2.Based on the constructed wire-driven soft robotic fish model,a dynamic terminal sliding mode controller is designed.The stability of the controller for the tail motion of the wire-driven soft robotic fish is proved by Lyapunov theory.The innovation of terminal sliding mode controller is that the nonlinear function is introduced into the design process of sliding hyperplane,and a dynamic linear sliding mode surface is constructed,which can make the tracking error on the sliding mode surface converge to zero in a finite time.The simulation results show that the controller can track the input sine curve quickly and verify the accuracy of the model.Compared with the traditional sliding mode controller,the response speed is faster and the chattering problem is eliminated.3.Based on the proposed design of the wire-driven soft robotic fish,appropriate materials and hardware are selected to make the soft fish tail.Through the hardware and software design of single-chip microcomputer control system,the control of the soft fish tail is realized.The soft fish tail is made of low-hardness silicone,which is poured into a mold made by 3D printing to be solidified.The command is issued by the host computer,which interacts with the control circuit through the serial port.Then the controller steers the motor to pull the driven-wire such that the swing of the fish tail is realized.Experiments show that the soft fish tail control system can generate oscillatory motion with different amplitudes and frequencies,and it is simple to implement,fast in response.The wire-driven soft robotic fish can complete underwater forward and steering experiments so that the effectiveness of the proposed design is verified.