Research On The Trajectory Tracking Control Strategy Of A Robotic Manipulator Based On Sliding Mode

With the continuous progress of science and technology,the field of robotics has been developing rapidly.As an important part of robotics,robotic manipulators can be used in different fields,such as industrial manufacturing,safety,and aerospace technology.In order to ensure the safe operation of the manipulator system,its control problem has become a hot research topic in the field of automation.However,because the manipulator system is a nonlinear time-varying system,there are complex disturbance uncertainties(such as external unknown disturbances and model parameter errors),which will seriously reduce the accuracy of its trajectory tracking.Meanwhile,in recent years,the task requirements for the robotic manipulator system have become increasingly complex,and in order to accomplish the task,the robotic manipulator system also puts forward higher requirements on convergence speed and tracking accuracy.Considering that most of the current control schemes can only make the robotic manipulator system converge asymptotically,the convergence time tends to infinity,and there are problems with the convergence speed being too slow,the chattering being too large,and the use in practice being somewhat limited.Aiming at the above problems,this thesis mainly studies the finite time/fixed time trajectory tracking control method and applies the designed control method to the trajectory tracking control of the manipulator.The main work of this thesis is as follows:(1)For the robotic manipulator system with external disturbances and model errors,a finite-time control scheme based on adaptive super-twisting is designed to effectively reduce the chattering problems in the sliding mode control.The scheme first establishes a robotic manipulator dynamics model,followed by the design of a finite-time disturbance observer to effectively estimate the composite disturbance.Secondly,considering that the reaching law of the traditional sliding mode control contains discontinuous switching terms and that there will be excessive chattering when the system state approaches the sliding mode surface,this thesis designs an adaptive super-twisting method to ensure the continuity of the control law and reduce the chattering.Finally,the finite-time stability of the closed-loop system is proved by a rigorous theoretical analysis,and the superiority of the control scheme is verified by numerical simulation.(2)Aiming at the problem that the convergence time of the finite time control algorithm of a nonlinear manipulator depends on the initial state of the system,a fixed time control method is designed.Firstly,for the problem that the upper bound of convergence time of the existing fixed-time stable system is conservative,a new linear term is introduced in this thesis,and a new fixed-time stable system is designed.Based on this system,sliding mode surface and reaching law are designed.Further,considering the problem that the upper bound of the compound perturbation of the robotic manipulator system is difficult to determine,a new adaptive law is proposed to estimate its upper bound,while the hyperbolic tangent function is introduced to maintain the continuity of the control law and reduce the chattering existing in the sliding mode control.Then,the fixed-time stability of the closed-loop control system is verified by rigorous theoretical analysis.The simulation results show that the manipulator system can achieve high-precision tracking control of the desired trajectory with an unknown interference upper bound.(3)A fixed-time fault-tolerant control scheme is proposed for a robotic manipulator system with actuator failures,model parameter errors,unknown external perturbations,and friction.Firstly,a novel fixed-time stable system is proposed that can effectively adjust the convergence rate and the magnitude of the power term coefficient of the system state regardless of whether the system state is far from or near the equilibrium point,and the upper bound of the convergence time is proved by a rigorous theoretical analysis.At the same time,considering the complex disturbance in the manipulator system,a fixed-time interference observer is designed that can approximate the complex disturbance within a fixed time,and then the feedforward compensation system can improve the accuracy.In addition,a fixed-time stability analysis of the closed-loop system is performed by Lyapunov functions,and it is demonstrated that the upper bound of the convergence time is only determined by the control parameters.Finally,the superiority of the designed control method is verified by numerical simulation results.