Research On Several Typical Sliding Mode Controllers Of High Speed Ball Screw Drives

The ball screw feed system is a key component in the machine tool,which affects the machining accuracy of the workpiece.The ball screw feed system is a complex electromechanical system which has various disturbances.This paper analyzes the dynamic characteristics of the ball screw feed system,considers the disturbances and time-varying uncertainties,and establishes a mathematical model with uncertain parameters that can reflect its real characteristics.Based on the flexible body model with uncertain parameters of the ball screw feed system,several controllers are designed,which can reduce the impact of unknown disturbances and dynamic changes.The control methods designed in this paper have been verified by simulations and experiments,which proves their effectiveness.The main work and innovations of this paper are as follows:1)The working principle and key control issues of the machine tool and ball screw feed system are introduced.The specific conditions of the laboratory equipment and research objects are introduced.The dynamic characteristics of the ball screw feed system during operation,as well as the uncertainties and unknown disturbances,are analyzed.Through the kinematics equation,a flexible body model and a rigid body model are established.Considering the time-varying dynamic,a time-varying flexible body model with uncertain parameters is established.The typical P-PI control method and adaptive sliding mode control method are used to design controllers for the rigid body model.Simulation analysis and experimental verification are performed to prove the effectiveness of the model.2)Considering the time-varying uncertainties and disturbances,a robust H? integral sliding mode controller based on parameter uncertainty model is proposed.Compared with the rigid body model,the parameter uncertainty model can more accurately reflect the source of the system error.Ordinary sliding mode structures can introduce steady-state errors,and integral sliding mode can be stable.The robust H? control method can be used to compensate the uncertain factors and unknown disturbances in the system,which can improve the parameters of the sliding mode function,and obtain an optimized controller.According to the simulations and experiments,it is found that the proposed method is robust to the disturbances and can improve the control precision.3)Considering the mismatch disturbances in the system,an adaptive sliding mode controller with exponential disturbances observer is designed.Due to the friction and nonlinear noise disturbances in the system,the control accuracy is affected.The improved exponential convergence nonlinear disturbances observer can effectively observe the matched and unmatched disturbances in the system.Aiming at the discontinuity of the existing approach law,an improved approach law is designed.Theoretical and simulation analysis prove that the observer can accurately track the disturbances of the observation system,and the convergence speed of the improved observer is optimized.Simulations and experiments show that this method can suppress disturbances and greatly improve the control accuracy.4)Aiming at improving the convergence speed and robustness,a nonlinear terminal sliding mode control method was designed which can improve the approach law.The nonlinear sliding mode structure has a faster convergence speed and causes the error to converge to zero in a finite time.The improved approach law can avoid the jitter problem caused by the traditional switching function.An error function for specified performance convergence can ensure that the tracking error remains within a certain range and can converge quickly.By combining the specified performance error function with the terminal sliding mode function,a controller with higher control accuracy and robustness is obtained.The analysis proves that the method satisfies the Lyapunov theorem.The effectiveness is verified by simulations and experiments.