| The research content of this paper is one part of the National Natural Science Foundation of China"the design and research of a new amphibious spherical robot(51175048)."It mainly studies the motion control of underwater spherical robot.The nonlinear controllers are designed for the common motion of BYSQ-3 spherical underwater robot,the designed controller have good stability,fast response,strong anti disturbance etc.,the control method can improve the performance of traditional asymptotically stable control strategy,more easy to implement in engineering.It provides theoretical basis and technical guarantee for underwater robots to accomplish various tasks with high quality.The controllers can also be extended to land mobile robots and space flying robots.In details,this paper mainly studies the following aspects:(1)By using Newton's laws of motion,the earth-fixed frame and the body-fixed frame of underwater robot are established,the statics and dynamics characteristics of the underwater spherical robot are analyzed.Considering the factors of underwater robot such as gravity,buoyancy,hydrodynamic force,Coriolis centripetal force and restoring force,interference force,the simplified 6 degree of freedom model and 3 degrees of freedom horizontal model are established.(2)The point stabilization problem for the underwater spherical roving robot(BYSQ-3)in the horizontal plane is addressed.The finite-time stable control laws are adopted to steer the robot to the origin fastly?accurately and reliably.Firstly,the inner structure and operational principle of the robot is described and the kinematic and dynamic equations are established.Secondly,the diffeomorphism transformation and change of inputs are introduced to decouple the multivariable coupling system into two subsystems.The second subsystem consists of two double integrator systems.The finite-time controller is introduced to ensure part states converge to zero in finite time.Then,the other states are steered to the origin using the same method.Thirdly,the design process has no virtual input and the stability analysis is simple,the controller designed is easy for engineering implementation.The simulation and experiment results are presented to validate the shorter convergence time and better stability character of the controller.(3)The point stabilization motion control method of underwater spherical robot based on the power integral technique is studied.The hydrodynamic coefficients of the system are analyzed by CFD technology,and the finite time stabilization control strategy based on backstepping is adopted.Through the reversible transform,multi variable nonlinear dynamic equations of the system is divided into two cascaded form subsystem.The first subsystem is composed of two state variables,the second subsystems is composed of two double integral system,for the second subsystem,we designed the finite time stabilization controller which contained two stage.Each stage can ensure the two state variables finite time convergence.Finally the designed controller can guarantee all the state variables converge to the origin in finite time and the coupling phenomenon completely disappeared.The complexity of the system is reduced.Because the gain and the power index both can be adjusted,it is easy to implement in engineering.The finite time stabilization control the law has the advantages of fast convergence and strong anti-interference.The results of numerical simulation and pool test confirm that the controller has fast convergence and good stability.(4)The curve path tracking control strategy of underwater spherical robot is studied.We transform the dynamic equation of the underwater vehicle into a nonlinear cascade system,and design a finite time controller for underwater vehicle path tracking innovatively.The finite time control method of cascade system is not only suitable for underwater spherical robots,but also for other mechanical systems.This control strategy can also be directly extended to other types of non holonomic mechanical systems.Compared with the traditional asymptotically stable controller,the finite time controller can reduce the coupling degree and shorten the convergence time.The simulation results show that the designed finite time controller has good performance.Based on the simulation results,we have carried out the real world experimental test,and validated the effectiveness of the finite time controller.(5)Research on the control method of nonlinear finite time stabilization of spherical robot under water level track,through the study of the tracking error dynamics model of track,the kinetic equation is divided into two parts,using coordinate transformation into dynamic equation of motion error is with low coupling equation,the velocity error as the virtual controller town location error then,the drive motor to achieve stabilization of speed error,respectively,using the theory and the terminal sliding mode control method for cascade system nonlinear control,by introducing the integral term in the controller,the error size tracking in finite time convergence to the origin,and has a high precision.The breakthrough of traditional design method can only reach the infinite horizontal convergence limit of progressive convergence or exponential convergence,and achieve high precision fast track tracking control.(6)The attitude control system of underwater vehicle based on four element number description is studied.Aiming at the attitude control problem of underwater vehicle,a controller based on two order integral sliding mode adaptive gain is designed in this paper,which is a discontinuous finite time controller.The designed adaptive law can update the gain of the controller by this method without the need to know the value of uncertainty and external disturbance in advance.From the simulation results,the controller can avoid the over adaptation of the controller gain.The controller is globally robust and finite time stable,and the finite time stability is proved by the homogeneous theory.It is worth noting that the two order integral sliding mode is introduced to make the system smaller.It can be seen from the comparative data in the paper that compared with other control strategies,the control strategy has higher steady-state accuracy and faster convergence speed.The actual swimming pool experiment also shows the effectiveness of the controller.Through the above research,we initially grasp the basic motion control theory of underwater spherical exploration robot,the finite time motion controllers for common movement patterns of the spherical underwater robot are designed and and the strict theoretical deduction and proof are carried out.Numerical simulation and pool experiments verify the effectiveness of these controllers.The design methods of these finite time controllers can also be extended to other two order nonholonomic systems. |
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